| N | Speeker | Institution | Abstract Title | Abstract Text |
|---|---|---|---|---|
| 1 | Alex Blatov | MISiS | - | - |
| 2 | Maksim Parfenov | Russian Academy of Sciences Landau Institute for Theoretical Physics | Spin-to-integer quantum Hall effect crossover in topological superconductors | Recently, the study of criticality in quantum systems has attracted significant interest. There is theoretical evidence suggesting the existence of the spin quantum Hall effect (sqHe) in two-dimensional superconducting systems with d_(x^2-y^2 )+i d_xy [1]. In such systems, the quantization of spin conductivity (in even integers of e^2/h) has been demonstrated. Since the sqHe is closely related to the integer quantum Hall effect (iqHe), it is natural to consider whether certain symmetry-breaking mechanisms could induce a crossover between them [2]. In this study [3], we develop a theoretical framework for the crossover from the spin quantum Hall effect to the integer quantum Hall effect. First, we analyze the edge theory of a d_(x^2-y^2 )+i d_xy topological superconductor, as derived in [1]. We demonstrate that the presence of static disorder at the edge leads to the emergence of a topological theta term in the effective diffusive action. This indicates that the quantization of spin conductance remains robust against impurities, and the corresponding action falls within class C of the Altland-Zirnbauer classification [4]. We further show that applying a Zeeman field only at the edge is insufficient to induce a crossover. Next, we examine the bulk (2D) action for class C in the presence of Zeeman symmetry breaking. We show that bulk topological excitations (instantons) change across the crossover. Specifically, we find that instantons with topological charge W=1 are suppressed by the Zeeman field, while instantons with W=2 transform into two Pruisken instantons [5] with W=1. As a result, the quantization of spin conductivity transitions from even integers to all integers. We propose that this spin-to-integer quantum Hall effect crossover could potentially be realized in topological superconductors, such as twisted Bi_2 Sr_2 CaCu_2 O_(8+x). *This work was supported by the Project No. FFWR-2024-0017. [1] T. Senthil, J. B. Marston, and M. P. A. Fisher, Spin quantum Hall effect in unconventional superconductors, Phys. Rev. B 60, 4245 (1999). [2] S. Bhardwaj, I. A. Gruzberg, and V. Kagalovsky, Relevant perturbations at the spin quantum Hall transition, Phys. Rev. B 91, 035435 (2015). [3] M. V. Parfenov, I. S. Burmistrov to be published. [4] A. P. Schnyder, S. Ryu, A. Furusaki, and A. W. W. Ludwig, Classification of topological insulators and superconductors, AIP Conf. Proc. 1134, 10 (2009). [5] A. M. M. Pruisken, Quasiparticles in the theory of the integral quantum Hall effect (I), Nucl. Phys. B 285, 719 (1987). |
| 3 | Boris Eremin | Skoltech, MIPT, IITP RAS | Conformal bootstrap and A-D-E construction in Gepner Models | We construct N=2 Superconformal Field Theories with modular invariant partition functions and with central charge c=9. Such theories arising after the compactification in superstring theory. Left and right primary fields in these theories are connected according to A-D-E classification. Orbifolds of the product of Minimal Models connected to Calabi-Yau manifolds of Fermat types are considered. We construct the set of mutually local fields, twisted by the elements of the group of symmetry. |
| 4 | Asya Aynbund | MIPT | Scalar Field Action under 4D Isotropic Cut-off and its Cosmological Impact | Specific action for isotropic fluctuations of scalar field is derived under the condition of 4D cut-off. It is implemented into the estimates of dark energy scale consistent with current cosmological data. |
| 5 | Igor Burmistrov | Landau | Test | Test |
| 6 | Dmitriy Shapiro | Forschungszentrum Jülich, Germany | Quantum Simulation of the Dicke-Ising Model via Digital-Analog Algorithms | The Dicke-Ising model, one of the few paradigmatic models of matter-light interaction, exhibits a superradiant quantum phase transition above a critical coupling strength. However, in natural optical systems, its experimental validation is hindered by a \"no-go theorem\". Here, we propose a digital-analog quantum simulator for this model based on an ensemble of interacting qubits coupled to a single-mode photonic resonator. We analyze the system\\'s free energy landscape using field-theoretical methods and develop a digital-analog quantum algorithm, which disentangles qubit and photon degrees of freedom through a parity-measurement protocol. This disentangling enables the emulation of a photonic Schrödinger cat state -- a hallmark of the superradiant ground state in finite-size systems. The cat state can be unambiguously probed through the Wigner tomography of the resonator\\'s field. Our algorithm features a sequence of analog Jaynes-Cummings gates combined with standard digital single-qubit and two-qubit rotations. This quantum circuit is capable of simulating quench dynamics and the quantum phase transition between the normal and superradiant phases. Additionally, we (i) applied a path-integral description to the model via the bosonic angular representation of spin operators and (ii) formulated a quasi-classical description of fluctuations in the large-spin limit. This approach can be useful for further studies of macroscopic quantum tunneling. Finally, we found that the qubit-qubit interaction leads to an emergent Ising transition driven by the Kibble-Zurek mechanism in imaginary time. The qubit subsystem becomes critical for certain quantum trajectories of the photon field, making the fluctuations in the superradiant phase non-trivial, in contrast to the conventional Dicke model. For further details, see our preprint [1]. [1] D. S. Shapiro, Y. Weber, T. Bode, F. K. Wilhelm, D. Bagrets, \"Quantum Simulation of the Dicke-Ising Model via Digital-Analog Algorithms\", arXiv:2412.14285 (2024). |
| 7 | Soumya Bera | Indian Institute of Technology Bombay, India | Pre-localization from fock space fragmentation into resonances | Many-body localization arises from the interplay of interactions and disorder in closed quantum systems, forming an emergent integrable phase, which could have potential applications in modern quantum technologies. In recent years, significant progress has been made in understanding the fragility of the phase, mainly when studied through ensemble-averaged properties within a reasonable parameter regime. A key insight from these studies is the presence of strong sample-to-sample fluctuations in local observables, such as particle density. Here, we take a Fock-space perspective on thermalization dynamics, developing a geometric description of Fock-space connectivity that dominates transient dynamics. Even in the weak disorder regime, certain strongly localized samples can be understood as fragmented Fock-space clusters onto dynamically resonant structures. This highlights the complexity of disorder ensembles, questioning the notion of many-body localized phase in generic model. |
| 8 | Artem Alexandrov | Moscow Institute of Physics and Technology | Classical phase-locking phenomena and its quantum interpretation | We discuss how the classical phase-locking phemomena arises in quantum mechanical systems. We provide the correspondence between the Poincare rotation number for the 2D dynamical systems on torus of Mobius type and the Schrodinger equation with periodic potential. This correspondence allows us to treat slow-fast dynamics in systems on torus in terms of exact WKB and vice-versa |
| 9 | Grigory Budkin | Ioffe Institute | Ballistic and shift contributions to the photogalvanic effect under Coulomb interactions | We report on the theoretical study of photocurrents arising in direct optical transitions in semiconductor bulk materials and structures taking into account the Coulomb interaction. In macroscopically homogeneous crystals or laterally uniform two-dimensional systems lacking inversion symmetry, an alternating electromagnetic field can induce a steady photocurrent, a phenomenon known as the photogalvanic effect. We develop a theory of the linear interband photogalvanic effect that precisely accounts for the electron-hole Coulomb interaction. For the interband optical transitions, there are two contributions to the linear photocurrent: the shift contribution, caused by the displacement of electron wave packets in the real space during quantum transitions, and the ballistic contribution, originating from asymmetry of the photoelectron distribution in the momentum space. While recent studies of the linear photogalvanic effect have been predominantly focused on the shift contribution [1, 2], it is emphasized in Ref. [3] that the ballistic contribution dominates for interband transitions. We present calculations comparing both contributions within a unified band-structure model for systems of different dimensions. A detailed microscopic theory of shift and ballistic currents is developed, incorporating a self-consistent method to treat Coulomb correlations between the photoexcited electron and hole to all orders of perturbation [4]. The theory is applied to calculate the linear photogalvanic effect in bulk semiconductors with a zinc blende lattice, as well as in two-dimensional materials based on monolayers of transition metal dichalcogenides of the D3h symmetry. It is demonstrated that the Coulomb interaction enhances the shift photocurrent due to an increase in optical absorption due to excitonic effects, although the shift current does exist even neglecting electron-hole scattering. In contrast, the ballistic contribution to the linear photogalvanic effect for direct optical transitions requires an additional scattering to take place, here the Coulomb scattering of a photoexcited electron by a hole. The matrix elements of the velocity operator taken between the Coulomb two-particle functions of the continuous spectrum, including its components off-diagonal in the wave vectors, are calculated in order to obtain the ballistic contribution. Frequency dependencies of the both contributions to the photocurrent are calculated for bulk semiconductors as well as for two-dimensional monolayer structures. It is demonstrated that the ballistic photocurrent can significantly exceed the shift current in both material classes. It is shown that the ratio of the ballistic contribution to the shift contribution scales as l/aB, where l is the charge carriers mean free path and aB is the exciton Bohr radius. As a result, in a wide range of frequencies where the mean free path of photoexcited charge carriers is longer than the Bohr radius, the ballistic contribution dominates. Thus, accounting for Coulomb interaction to the ballistic mechanism yields a substantially larger total photocurrent than shift-only models predict. This work was supported by the Russian Science Foundation (project 22-12-00211). 1. Z. Dai and A. M. Rappe // Phys. Rev. B 104, 235203 (2021). 2. Zhenbang Dai and A. M. Rappe // Chem. Phys. Rev. 4, 011303 (2023). 3. B. I. Sturman // Phys.-Usp. 63, 407 (2020). 4. G. V. Budkin, E. L. Ivchenko // JETP 167, 279 (2025). [arXiv:2409.05571] |
| 10 | Maxim Shishkin | Landau Institute for Theoretical Physics RAS | Dynamics of vesicles under stretching | Closed lipid membranes (vesicles), being flexible and incompressible, demonstrate a plethora of non-spherical shapes (especially under simple external influences). Within the framework of the hydrodynamic approach, the bilayer is treated as an infinitely thin liquid film with a surface density of free energy. The starting point for this consideration is Helfrich\\'s energy [W. Helfrich, Z Naturforsch (1973)] , which depends on vesicle shape. Using hydrodynamic Poisson brackets, we can obtain a non-dissipative contribution to the stress tensor from the membrane. Corresponding surface forces cause flows in the viscous surrounding liquid which make the membrane to move. Although such flows occur at low Reynolds numbers, described by the linear hydrodynamic equation (the Stokes equation), vesicle\\'s shape changes significantly over time.. This makes the system of dynamic equations highly nonlinear. On the one hand, it determines the complexity of the problem, and on the other hand, leads to the need for numerical modelling of the process. The study investigates the behavior of elongated vesicles under the influence of extending forces, such as uniaxial flow and optical tweezers. There are two critical values of force amplitude: beyond the first, a \"dumbbell\"-shaped structure forms with a possible infinite elongation, and the second is responsible for the so-called pearling instability, i.e., the formation of beads connected by thin tubes. We also provide a qualitative description of the phenomenon by discussing the variety of stretched shapes and conditions of quasi-stationarity and transition to infinite stretching. In addition, we study the highly nonlinear stage: a slow dynamics remains after the formation of pearls due to the thinness of tubes. Our results qualitatively agree with experimental observations [Kantsler, Segre, and Steinberg (2008)]. |
| 11 | Aleksey Lunkin | Nanocenter CENN | Local Density of States Correlations in the Lévy-Rosenzweig-Porter random matrix ensemble | We present an analytical calculation of the local density of states correlation function β(ω) in the Lévy-Rosenzweig-Porter random matrix ensemble at energy scales larger than the level spacing but smaller than the bandwidth. The only relevant energy scale in this limit is the typical level width Γ. We show that β(ω≪Γ)∼W/Γ (here W is width of the band) whereas β(ω≫Γ)∼(W/Γ)(Γ/ω)^μ where μ is an index characterising the distribution of the matrix elements. We also provide an expression for the average return probability at long times: ln[R(t≫Γ)]∼−(Γt)^μ/2. Numerical results based on the pool method and exact diagonalization are also provided and are in agreement with the analytical theory. |
| 12 | Gleb Seleznev | Landau Institute for Theoretical Physics (RAS) | Enhancement of Superconductivity in Dirty Films in an External Magnetic Field | Thin dirty superconducting films containing magnetic impurities exhibit nontrivial behavior when subjected to an applied magnetic field. This behavior manifests itself in the enhancement of superconductivity, which is attributed to the reduction in the exchange scattering rate due to the polarization of the impurity spins in the presence of the magnetic field. This effect was theoretically predicted in Ref. [1] and then observed experimentally in Ref. [2]. In both studies, the authors concentrated on the dependence of the critical temperature on the magnetic field parallel to the film surface, revealing a nonmonotonic behavior characterized by a maximum at finite field values. However, manifestations of this enhancement for other observable physical quantities, as well as the description of the effect in the presence of a magnetic field component perpendicular to the film surface, have not been investigated. To address this gap, we develop a theoretical framework employing Gorkov\\'s diagrammatic technique for superconductors. Our work expands the theory of Ref. [1] in two directions: (i) we demonstrate that the enhancement is also reflected in an increase in superfluid density and the spectral energy gap; (ii) we reveal a nonmonotonic dependence of the second critical field (perpendicular to the film surface) on the magnetic field component parallel to the surface. [1] M.Yu. Kharitonov and M.V. Feigelman, \"Enhancement of superconductivity in disordered films by parallel magnetic field\", JETP Lett. 82, 421–425 (2005). [2] Masato Niwata, Ryuichi Masutomi and Tohru Okamoto, \"Magnetic-Field-Induced Superconductivity in Ultrathin Pb Films with Magnetic Impurities\", Phys. Rev. Lett. 119, 257001 (2017). |
| 13 | Artem Posadskii | Lebedev Physical Institute of the Russian Academy of Sciences | Effective action of the Γ-subsystem of the Ising superconductor | The work is devoted to superconductivity in recently discovered Ising superconductors. This state in them has not yet been fully studied. In particular, the question arises as to which of the valleys in the Brillouin zone play the main role. The central valley Γ is, under certain assumptions, an independent electron subsystem. In the work, we have obtained and analyzed the gauge-invariant effective action of this subsystem. It includes singlet and triplet pairings, and it is necessary to take into account the locality of these interactions, as well as the symmetry of the lattice. In particular, we obtain an expression for the superconducting weight in the subsystem. |
| 14 | Artem Polkin | L. D. Landau Institute for Theoretical Physics | Conductivity of a superconductor in presence of microwaves | Nonequilibrium properties of superconducting systems have been studied for a long time. One of such properties is enhancement of superconductivity by microwave irradiation, which was explained theoretically by Eliashberg [1,2] by means of Gorkov equations. In 2018 this theory was extended and refined in [3]. However, recently novel mechanism of microwave absorption was suggested [4]. In their paper authors introduce mechanism of absorption, similar to the Debye absorption in molecular gases, which for non-zero current leads to a large contribution to the ac conductivity, which is proportional to the inelastic scattering time $\\tau_{in}$. In present work, we consider quasi-one dimensional diffusive superconductor with finite current bias. Within Keldysh non-linear sigma model approach, we computed conductivity, which for small amplitude of microwave irradiation could be treated within linear response formalism. We found that in presence of dc current conductivity acquires a novel contribution, which is responsible for the so called Debye contribution to the conductivity. We calculated this term for a wide range of frequencies of a microwave and established that results are drastically different for small and large values of $\\omega$. [1] G. M. Eliashberg. Film superconductivity stimulated by a high-frequency field. Sov. Phys. JETP Lett., 11:186, 1970. [2] B. I. Ivlev and G. M. Eliashberg. Influence of nonequilibrium excitations on the properties of superconducting films in a high-frequency field. Sov. Phys. JETP Lett., 13:464, 1971. [3] K. S. Tikhonov, M. A. Skvortsov, and T. M. Klapwijk. Superconductivity in the presence of microwaves: Full phase diagram. Phys. Rev. B, 97:184516, May 2018. [4] M. Smith, A. V. Andreev, and B. Z. Spivak. Debye mechanism of giant microwave absorption in superconductors. Phys. Rev. B, 101:134508, Apr 2020. |
| 15 | Yuriy Dmitrievtsev | Landau Institute for Theoretical Physics (RAS) | Superconducting orbital diode effect in SN bilayers | In superconducting hybrid structures with broken geometric symmetry and symmetry with re- spect to time reversal, a diode effect occurs, which consists in different critical currents when an supercurrent flows in different directions. The system we are considering is an SN bilayer – two layers of superconductor (S) and normal metal (N) brought into contact. The bilayer is located in an external parallel magnetic field. The properties of the supercurrent flowing along the bilayer perpendicular to the magnetic field are studied. In 2023, an article [1] was published on the study of the diode effect in such a structure. In it, this effect in the MoN/Cu bilayer was studied nu- merically and experimentally. Numerical calculation and experiment were carried out for a bilayer with a thickness of each layer on the order of several coherence lengths, but thin compared to the London penetration depth, in the dirty limit allowing the application of the Usadel equations. The fact that the thickness of the layers is of the order of the correlation length leads to a nontrivial distribution of the order parameter, and hence the concentration of superconducting electrons along the thickness of the sample. This makes the problem analytically unsolvable in the general case. Our goal is to consider a similar system in extreme cases that allow an analytical solution, in which, nevertheless, many qualitative patterns for critical currents are preserved, as well as to consider the effect of interface resistance on the diode effect. In particular, the dependences of critical currents on the magnetic field are found. A nonmonotonic dependence of the efficiency of the diode effect on the resistance of the interface with the maximum at a certain optimal resistance has also been established. 1. Finite momentum superconductivity in superconducting hybrids: Orbital mechanism / M. Yu. Levichev, I. Yu. Pashenkin, N. S. Gusev, D. Yu. Vodolazov // Phys. Rev. B. — 2023. — Sep. — Vol. 108. — P. 094517. https://link.aps.org/doi/10.1103/ PhysRevB.108.094517. |
| 16 | Alexey Mikhaylenko | Moscow Institute of Physics and Technology, Lebedev Physical Institute, Skolkovo Institute of Science and Technology | Non-Gaussian Initial Correlations in Non-Equilibrium Quantum Field Theory | This work is devoted to the role of initial correlations in the nonequilibrium evolution of observables in quantum field theory. We show that information about the initial state of the system can be represented as an additional term in the Keldysh action. This term is expressed in terms of the generating functional of the cumulants of the initial Wigner functional. The presence of non-Gaussian correlations manifests itself in the form of additional vertices, each of which is proportional to the corresponding cumulant. Since, generally speaking, there can be infinitely many nonzero non-Gaussian cumulants, it becomes necessary to somehow limit ourselves to a finite number of them. We show that this can be achieved using the formalism of a two-particle irreducible (2PI) effective action. Namely, we demonstrate that only a finite number of cumulants contribute to the equations of motion in the approximation with a finite number of loops in the diagrammatic representation of an effective action. This makes it possible to systematically take into account the cumulants of higher degrees, gradually increasing the number of loops in approximation to effective action. In addition, we show how non-Gaussian initial correlations can generate a non-zero average field in the process of quantum evolution even if it’s value was zero at the initial moment of time. |
| 17 | Grachik Simonyan | Moscow Institute of Physics and Technology, Lebedev Physical Institute | Calculation of correlation functions for nonequilibrium quantum systems with non-Gaussian initial conditions | A non-perturbative technique within the Schwinger-Keldysh formalism is applied for nonequilibrium quantum systems with non-Gaussian initial conditions. The system has a free part in the form of an oscillator and a quartic interaction term. The correlation function is computed under specific non-Gaussian initial conditions using the Kadanoff-Baym equations in a two-loop approximation. The same results are also derived using perturbation theory, and a comparison is made between the two approaches. Additionally, we present integral-differential equations in phase space for multiple degrees of freedom, applicable to quantum field systems, and calculate the corresponding correlation function. |
| 18 | Sergey Potashin | Ioffe institute | Thermoelectric and viscous contributions to the hydrodynamic ratchet effect | We study the hydrodynamic regime of the ratchet effect, i.e., radiation-induced generation of a direct electric current, $J_{\\rm rat}$, in an asymmetric dual-grating gate structure without an inversion center. Recently, it was demonstrated that the frequency dependence of $J_{\\rm rat}$ is essentially different within the hydrodynamic (HD) and drift-diffusion (DD) regimes of electron transport: $J_{\\rm rat}^{\\rm HD} \\propto 1/\\omega^6$ and $J_{\\rm rat}^{\\rm DD} \\propto 1/\\omega^2$ for $\\omega \\to \\infty$. Here, we analyze the previously neglected thermoelectric contribution to the ratchet current, $J_{\\rm th}$, which arises due to inhomogeneous heating of the electron liquid. We demonstrate that this contribution dominates at sufficiently low electron-phonon scattering rates, yields a high-frequency asymptotic $J_{\\rm th} \\propto 1/\\omega^2$ even in the HD regime, and can change the sign of the response at certain frequency intervals. We analyze the plasmonic resonance in $J_{\\rm rat}$, which has the shape of an asymmetric Fano peak, and find that the asymmetry increases with increasing thermoelectric contribution. We also study the effect of finite viscosity of the electron liquid, as well as the manifestation of the plasmonic drag phenomena and inhomogeneous rectification effects in the ratchet current. We demonstrate that viscosity suppresses plasmonic resonance but unexpectedly enhances the Drude peak due to the interference nature of the ratchet effect. This work was supported by the Russian Science Foundation (project 25-12-00212) |
| 19 | ELIZAVETA SAFONOVA | Ljubljana University | Density correlation function L\'evy Rosenzweig-Porter model via supersymmetric approach | We present an analytical calculation of the density of states correlation function in the L´evy-Rosenzweig-Porter random matrix ensemble which off-diagonal elements are strongly non-Gaussian with power-law tails. In order to obtain the results on all the energy scales we use supersymmetry approach. Power-law distribution tails makes the standard Hubbard-Stratonovich transformation inapplicable to such problems. We used, instead, the functional Hubbard-Stratonovich transformation which allowed to solve the problem analytically for large sizes of matrices. |
| 20 | Valentin Mylnikov | Ioffe Institute | Critical slowing down in two-photon dissipative oscillator | In this study, we investigate the critical slowing down of dissipative phase transition, which is observed in a parametric oscillator with two-photon drive and both linear and nonlinear dissipation. Using the numerical calculations, complex P-representation and the perturbative, we determine the exponentially small eigenvalue of the Liouville operator that determines small relaxation of the system towards the steady state. Acknowledgment This research was supported by RSF (project No. 21-72-30020). |
| 21 | Mikhail Pavlov | LPI RAS | Classical Virasoro blocks with heavy and light operators | In this note we study differential equations for classical blocks with heavy and light operators from different perspectives. We present ODEs for the 4-pt blocks, generalizing the ODE for the 4-pt identity block, found by Fitzpatrick, Kaplan, Walters, and Wang. |
| 22 | Aleksei Radkevich | Lebedev Physical Institute | Gutzwiller trace formula for potentials with tunneling | Tunneling is a quantum phenomenon, the essence of which is that the wave function of a system in the course of its dynamics penetrates into the energetically inaccessible region of configuration space. This phenomenon is essentially semiclassical and can be described within the framework of the semiclassical approximation in quantum mechanics by solving the Schrödinger equation by the WKB method. At the same time, there is a wide class of systems for which the description of tunneling within the framework of the Feynman path integral is of interest, in particular, dissipative systems, where the description of the system using the wave function is completely impossible. In such systems, tunneling can be described using the path integral in imaginary time, where the so-called instanton solutions are responsible for tunneling; however, being tied to imaginary time, this formalism is suitable only for studying the characteristics of a system in a state of thermodynamic equilibrium and is not applicable to significantly nonequilibrium phenomena. Hence, it is necessary to develop an approach that takes into account instanton solutions in the framework of the path integral in real time. In this work, a step in this direction is made, consisting in generalizing the Gutzwiller trace formula (which is usually derived in the real-time formalism) for the density of states of a quantum-mechanical particle in a potential with tunneling. |
| 23 | Konstantin Turyshev | HSE University | Current-phase relation of an S-TI-S Josephson junction with a Majorana edge mode | We consider a long and narrow S-TI-S Josephson junction on top of a 3D topological insulator in magnetic field [1,2], surrounded by a layer of insulating magnetic material. Majorana zero modes are predicted to be localized at Josephson vortices in the junction, while the outer edge of the junction supports a 1D Majorana edge mode. Parity of the number of vortices inside of the junction determines the boundary conditions for the edge mode, and in the case of the odd number of vortices, the edge contains a Majorana zero mode. As the global phase difference between the superconductors is varied, the vortices move along the junction. When a vortex approaches the edge of the junction, corresponding Majorana zero mode may hybridize with the Majorana zero mode on the outer edge, acquiring non-zero energy and contributing to the current through the junction. Considering the edge mode scattering problem, we find analytical expression for the energy of Majorana zero modes hybridization. We also discuss the current contribution of the hybridization of higher-energy modes, based on numerical solutions. References [1] Potter A. C., Fu L., Phys. Rev. B 88, 121109 (2013) [2] Yue G. et al.., Phys. Rev. B 109, 094511 (2024) |
| 24 | Viacheslav Krivorol | Institute for Theoretical and Mathematical Physics and Steklov Mathematical Institute, Moscow | First-order GLSM construction in sigma models | Sigma models form a class of field theories that play a crucial role in various branches of modern theoretical and mathematical physics. However, studying these models is challenging due to the highly nonlinear nature of their Lagrangians. There are some specific methods, such as the background field method, that can be used to study these models, but they have some limitations. There is an alternative recently proposed method, called \"the first-order GLSM formulation\" (or \"Gross-Neveu formalism\"), for studying sigma models. In this method one cast these models as gauge theories with a finite number of interactions using the idea of symplectic reduction. I will present how this method works for target spaces that are homogeneous Hermitian complex spaces associated with classical Lie groups. Based on joint works with Dmitri Bykov: https://arxiv.org/abs/2306.04555, https://arxiv.org/abs/2407.20423, see also https://arxiv.org/abs/2502.07612 |
| 25 | Ilya Gorbenko | Ioffe Institute | Current-induced instability in 2D electron liquid | Several possible mechanisms of current-induced instability have been discovered in 2D electron liquid: amplification of plasma waves due to asymmetric boundary conditions of Dyakonov and Shur [1], change of sign of the radiative decay rate resulting in negative absorption coefficient [2], Cherenkov-type instability arising when drift velocity of current exceeds plasma wave velocity [3] and interplay of different dispersion laws of gated and ungated plasmons [4]. We investigate current-induced plasma wave instability in 2D electron liquid with periodically modulated concentration which creates lateral plasmonic crystal (LPC), recently discussed in [5]. We found that solutions with largest instability increment are excited in particular interval of currents, which is fully determined with electron concentration profile. In this regime, three types of unstable solutions were discovered: the Cherenkov-type instability ω=ω_I+i λ_I with a small increment (ω_I≫λ_I), a new type of unstable solutions with a large increment ω=ω_II+i λ_II (λ_II>ω_II), and a purely imaginary solution ω=i λ_III. Increase of current outside the interval preserves only the first Cherenkov-type instability. This work was supported by the Russian Science Foundation (project 25-12-00212). [1] Dyakonov, Shur // PRL 71, 2465 (1993). [2] Mikhailov // PRB 58, 1517 (1998). [3] Kachorovskii, Shur // APL 100, 232108 (2012). [4] Petrov, Svintsov, Ryzhii, Shur // PRB 95, 045405 (2017). [5] Gorbenko, Kachorovskii // PRB 110, 155406 (2024). |
| 26 | Anton Selemenchuk | St.Petersburg State University, The Euler International Mathematical Institute | Fluctuations of Young diagrams for symplectic groups and semiclassical orthogonal polynomials | Consider an $n\\times k$ matrix of i.i.d. Bernoulli random numbers with some value of $p$. Dual RSK algorithm gives a bijection of this matrix to a pair of Young tableaux of conjugate shape, which is manifestation of skew Howe $\\GL_{n}\\times \\GL_{k}$-duality. Thus the probability measure on zero-ones matrix leads to the probability measure on Young diagrams proportional to the ratio of the dimension of $\\GL_{n}\\times \\GL_{k}$-representation and the dimension of the exterior algebra $\\bigwedge\\left(\\CC^{n}\\otimes\\CC^{k}\\right)$. Similarly, by applying Proctor\\'s algorithm based on Berele\\'s modification of the Schensted insertion, we get skew Howe duality for the pairs of groups $\\Sp_{2n}\\times \\Sp_{2k}$. In the limit when $n,k\\to\\infty$ $\\GL$-case is relatively easily studied by use of free-fermionic representation for the correlation kernel. But for the symplectic groups there is no convenient free-fermionic representation. We use Christoffel transformation to obtain the semiclassical orthogonal polynomials for $\\Sp_{2n}\\times \\Sp_{2k}$ from Krawtchouk polynomials that describe $\\GL_{2n}\\times\\GL_{2k}$ case. We derive an integral representation for semiclassical polynomials. The study of the asymptotic of this integral representation gives us the description of the limit shapes and fluctuations of the random Young diagrams for symplectic groups. The studied problem is closely connected with describing the moduli space of isomonodromic deformations of rational d-connections as a Sakai surface for discrete Painlevé equations. |
| 27 | Daniil Lopatin | Moscow Institute of Physics and Technology / Skolkovo Institute of Science and Technology | Local quantum quench in interacting field theories | Nonequilibrium quantum field theory is an important area of modern physics, where many arising problems require consideration of the unitary evolution of observables from some initial state of the system, which is not, generally speaking, an proper state for the corresponding Hamiltonian. In this case, the system, being in a nonequilibrium initial state, evolves over time to some equilibrium. One way to specify an initial nonequilibrium state is to instantly change the parameters of the system at the initial moment of time. In such case of creating nonequilibrium, we speak of a quantum quench. In this paper, we study the evolution of a quantum scalar field (and others) as a result of a local quantum quench, i.e. as a result of a rapid perturbation in the vicinity of a certain point. The problem is studied in the formalism of the Keldysh technique, which is convenient for considering nonequilibrium quantum systems. We study the semiclassical approximation, which is exact for non-interacting systems. To calculate the values of observables in the semiclassical approximation, a numerical code is used that calculates a functional integral using the Monte Carlo method. In the general case, to find a semiclassical solution, it is necessary: Find classical trajectories as functions of the initial conditions Calculate the desired observables on the obtained trajectories Average the obtained expressions over the initial conditions with a weight specified by the Wigner functional corresponding to the problem being solved By considering various types of quantum local quenches for various initial states, we study the properties of the corresponding system when a disturbance propagates in it. |
| 28 | Mikhail Sharov | MSU ITMP & INR RAS | Horndeski theory on a dynamical spherically-symmetric background | We study the stability of classical solutions in Horndeski theory. In this work, we address a general dynamical spherically symmetric background. We derive the set of stability conditions in the cubic subclass of Horndeski theory and formulate the no-go theorem for this subclass. For full Horneski theory and beyond Horndeski theory we formulate a set of linear stability conditions for high energy odd parity perturbation modes above an arbitrary solution. In this general setting we derive speeds of propagation in both radial and angular directions for gravity waves and compare them with the speed of light in the case of minimally coupled photon. In particular, we find that the class of beyond Horndeski theories, which satisfy the equality of gravity waves’ speed to the speed of light over a cosmological background, feature gravity waves propagating at luminal speeds above a time-dependent inhomogeneous background as well. We revisit the models recently derived from a Kaluza-Klein compactification of higher dimensional Horndeski theory, where the resulting electromagnetic sector features non-trivial couplings to Horndeski scalar. In particular, this class of theories admits the electromagnetic waves propagating at non-unit speed, which in turn allows to relax the constraints on Horndeski theories following from multi-messenger speed test. In this work we prove that both gravitational wave and its electromagnetic counterpart propagate at the same, although non-unit, speed above an arbitrarily time-dependent, spherically symmetric background within the theories in question. Hence, we support the statement that several subclasses of Horndeski theories are not necessarily ruled out after the GW170817 event provided the photon-Galileon couplings are allowed. We also formulate the set stability conditions based on odd parity perturbations for an arbitraty solution within the discussed theoretical setting. |
| 29 | Maxim Chepurnoi | Moscow state university | Tau-functions beyond the group elements | Non-petrubative partition functions of quantum theories constitute a class of τ −functions, which satisfy Hirota’s bilinear identities. To make this statement general, there must be a proper definition of τ −function, that gives rise to a set of bilinear identities. In the classical definition of τ −function for integrable Toda or KP hierarchies, there is a restriction on matrix elements to be based on group elements with the following comultiplication ∆(g) = g ⊗ g. This restriction cannot be straightforwardly transferred to the q-deformed case because there are no group elements in q- deformed UEA, except for its Cartan subalgebra. The new approach to the τ −function is to remove the restriction on the group elements and replace it with X, where ∆(X) = \\sum(X′α ⊗ X′′α) . The main result of this work is the derivation of the set of bilinear identities and τ −functions for Uq (sl3) in both fundamental representations for non-group elements. |
| 30 | Ivan Ryzhkov | MSU | ФУНКЦИИ БЕЙКЕРА-АХИЕЗЕРА ДЛЯ ТВИСТОВАННЫХ ПРЯМЫХ В ПРЕДСТАВЛЕНИИ DIM-АЛГЕБРЫ (0,0) | Известно, что полиномы Макдональда являются собственными функциями релятивистского обобщения гамильтониана Калоджеро-Сазерланда. Данный гамильтониан принадлежит интегрируемой системе, соответствующей прямой в представлении DIM-алгебры с центральными зарядами (0,0). Для гамильтонианов данной интегрируемой системы можно построить общие собственные функции, называемые функциями Бейкера-Ахиезера. Выражение для функций Бейкера-Ахиезера, соответствующих вертикальному известно. Сложность составляет получение универсального выражения для коэффициентов таких функций для повернутых прямых. В данной работе будут рассмотрены подходы к получению «твистованных» функций Бейкера-Ахиезера с применением двойной аффинной алгебры Гекке (DAHA), определенной подалгебре которой оказывается изоморфна DIM в случае (0,0). |
| N | Speeker | Institution | Abstract Title | Abstract Text |
|---|---|---|---|---|
| 1 | Mikhail Skvortsov | |||
| 2 | Yakov Fominov | Superconducting diode effect | I will present a concise overview of the rapidly developing field of nonreciprocal effects in superconducting transport, also known as the superconducting diode effect. The essence of this phenomenon lies in the asymmetry of a system’s properties when a supercurrent flows in opposite directions. Such an effect requires the simultaneous breaking of time-reversal and inversion symmetries. The underlying physical mechanisms can vary significantly, including effects of magnetic (and, more specifically, exchange) fields, spin-orbit interactions, and geometric asymmetry of the system. These effects can lead to nonreciprocal charge transport both in systems homogeneous along the current direction and in Josephson junctions. The work was supported by the Russian Science Foundation (Grant No. 24-12-00357). Literature: [1] Ya.V. Fominov, D.S. Mikhailov, Asymmetric higher-harmonic SQUID as a Josephson diode, Phys. Rev. B 106, 134514 (2022). [2] G.S. Seleznev, Ya.V. Fominov, Influence of capacitance and thermal fluctuations on the Josephson diode effect in asymmetric higher-harmonic SQUIDs, Phys. Rev. B 110, 104508 (2024). [3] D.S. Kalashnikov, G.S. Seleznev, A. Kudriashov, Y. Babich, D.Yu. Vodolazov, Ya.V. Fominov, V.S. Stolyarov, Diode effect in Shapiro steps in an asymmetric SQUID with a superconducting nanobridge, in preparation. [4] Yu.A. Dmitrievtsev, Ya.V. Fominov, Superconducting orbital diode effect in SN bilayers, in preparation. [5] D.A. Chuklanov, Ya.V. Fominov, Diode effect in superconductors with spin-orbit interaction, in preparation. | |
| 3 | Vladimir Zyuzin | L. D. Landau Institute for Theoretical Physics | ||
| 4 | Yurii Makhlin | Bound states on Josephson vortices in planar topological junctions | Josephson vortices in planar junctions on top of a topological insulator material in weak magnetic fields may bind electronic states. The Dirac spectrum of surface states in the topological insulator produces subgap states in the junction, which correspond to Landau levels, with a Majorana mode at zero energy. These zero modes are carried by vortices, with their location controlled via the magnetic field and phase bias. Interference of local Josephson currents can be used to demonstrate the presence of MZMs as well as to probe their quantum state. At integer flux values, the standard Fraunhofer interference demonstrates vanishing critical current, and the observed non-zero critical current can be linked to contribution of MZMs. Moreover, in the Corbino geometry flux quantization allows to probe only integer flux values. However, similar effects may arise from imperfections, including nonuniform geometry. We discuss effects of the geometric disorder and compare them to experiments. We further analyze other possibilities to probe physics of the bound states including spectroscopy. | |
| 5 | Alexei Litvinov | |||
| 6 | Alexander Belavin | |||
| 7 | Kolya Nikolaev | |||
| 8 | Vadim Geshkenbein | Institute for Theoretical Physics, ETH Zurich, CH-8093 Zurich, Switzerland | Planar Josephson junctions made from atomically thin films exhibit poor transverse screening, causing the magnetic-field dependence of the Josephson current Ic(B) to deviate from the standard Fraunhofer pattern of conventional junctions. The relevant flux determining the oscillations in Ic(B) is not the usual flux Φλ = 2BWλL penetrating the junction but the larger flux ΦW = 2BW2, including the lead areas near the junction, with W the junction width. The envelope of the Fraunhofer-like pattern also differs, with maxima decaying slowly ∝1∕√B rather than the usual ∝1/B. Given the weak screening, the junction is highly sensitive to Pearl vortices in the leads. Vortices alter the phase pattern and affect the Josephson current. Thermal fluctuations can cause vortices to jump in and out of the leads, leading to shifts in the Fraunhofer-like pattern, as observed in the recent experiment. Our model quantitatively explains these jumps, whose timescale depends on magnetic field, current, temperature, and superfluid stiffness. At elevated temperatures, fast vortex jumps may wash out the Fraunhofer pattern well below Tc. By analyzing the timescale of these jumps, we can determine the superfluid stiffness and the Berezinskii-Kosterlitz-Thouless transition temperature of magic-angle twisted four-layer graphene. These values are in agreement with recent kinetic inductance measurements. | |
| 9 | Hrant Topchyan | |||
| 10 | Alex Kamenev | |||
| 11 | Ilya Gruzberg | |||
| 12 | Dima Gangardt | Limit shapes and their phase transitions: classical and quantum | I will present examples of Limit Shapes - the most probable macroscopic shape with sharp boundaries separating frozen and fluctuating regions - which arise in a variety of classical and quantum systems. I will explain a special role played by analytic functions defining a Riemann surface whose topology can be changed abruptly across phase transitions. Most of the examples are based on free fermionic models; however, recently we studied a notable exception from this rule - the Polytropic Gas with a power-law equation of state. The analytic approach to Emptiness Formation Probability in Politropic Gas will be discussed. [1] J. Pallister, D.M. Gangardt and A. Abanov, "Limit shape phase transitions: a merger of arctic circles", J. Phys. A 55, 304001, 2022 [2] James S. Pallister, Samuel H. Pickering, Dimitri M. Gangardt and Alexander G. Abanov, "Phase transitions in full counting statistics of free fermions and directed polymers", Phys. Rev. Research 7, L022008, 2025 [3] Alexander G. Abanov, Dimitri M. Gangardt, "Emptiness instanton in quantum polytropic gas", SciPost Phys. 18, 122, 2025 | |
| 13 | Andrea Cappelli | INFN and University of Florence, Italy | Bosonizations and dualities in 2+1 dimensions | We discuss two methods for relating bosonic and fermionic relativistic field theories in 2+1 dimensions, the Z_2 gauging and the flux attachment. The first is primarily a correspondence between topological theories. Its inverse map, fermionization, shows how spin structures and Z_2 fermion parity emerge from a bosonic theory equipped with a dual Z_2^(1) generalized symmetry. The second method, flux attachment, is obtained by coupling to a Chern-Simons theory, and is at the basis of Abelian dualities. We illustrate the two bosonizations with explicit results in a solvable semiclassical, yet non-trivial conformal theory. We also combine the two bosonizations to obtain further duality relations. |
| 14 | Igor Gornyi | Karlsruhe Institute of Technology | Scaling of many-body localization transitions: Fock-space correlations, spectral observables, and dynamics | Many-body-localization (MBL) models can be viewed as tight-binding models in manybody Hilbert space (Fock space). We study MBL transitions in a family of single-spin-flip spin-1 2 models. They include the one-dimensional (1D) chain with nearest-neighbor interactions and the quantum dot (QD) model with all-to-all pair interactions. In addition, we consider their modifications (uQD and u1D models) with removed correlations of the off-diagonal matrix elements, as well a quantum random-energy model (QREM) with no correlations at all. This allows us to explore the role of correlations between matrix elements of the effective Fock-space Hamiltonians in the scaling of MBL critical disorder Wc(n) with the number of spins n [1]. Our numerical results based on many-body spectral observables are in excellent agreement with analytical arguments predicting a power-law (with logarithmic factors) growth of Wc(n) for QREM, u1D, uQD, and QD models. This growth is in stark contrast to the 1D model, where Wc(n) is essentially independent of n. Our findings demonstrate that the scaling of Wc(n) for MBL transitions is governed by a combined effect of Fock-space correlations of diagonal and off-diagonal matrix elements. We further investigate [2] the Fock-space and real-space dynamics in the single-spin-flip models. Specifically, we focus on the generalized imbalance that characterizes propagation in Fock space out of an initial basis state and, at the same time, can be efficiently probed by real-space measurements. For all models considered (1D, QD, and QREM), the average imbalance and its quantum and mesoscopic fluctuations provide excellent indicators for the position of the MBL transition Wc(n). The obtained results are in full consistency with those obtained from spectral observables [1]. We thus determine phase diagrams of the MBL transitions in the n-W plane, with clear evidence for a direct transition between the ergodic and MBL phases for each of the models, without any intermediate phase. We also determine the scaling of the transition width ∆W (n)/Wc(n) and estimate the system size n needed to study the asymptotic scaling behavior. Our results indicate the feasibility of experimental studies of n-W phase diagrams and scaling properties of MBL transitions in models of 1D and QD type and their extensions to other spatial geometry or distance-dependent interactions. [1] T. Scoquart, I.V. Gornyi, and A.D. Mirlin, Phys. Rev. B 109, 214203 (2024). [2] T. Scoquart, I.V. Gornyi, and A.D. Mirlin, arXiv:2502.16219. |
| 15 | Moshe Goldstein | Entanglement with symmetry: From record high to record low | Symmetries and the corresponding conservation laws, as well as entanglement, are two central pillars of quantum many body physics and field theory. Only relatively recently their interplay started to be studies by our group and others. In this talk I will provide two examples, showing that such an interplay can lead to both record-low and record-high entanglement. The first example concerns lattice gauge theories, which play a central role in high energy physics, condensed matter physics, and quantum error correction. Due to the nontrivial structure of the Hilbert space of such systems, entanglement is tricky to define. However, when one limits oneself to superselection resolved entanglement, that is, entanglement corresponding to specific gauge symmetry sectors, the entanglement becomes well-defined. Moreover, when gauge symmetry is strictly obeyed, superselection-resolved entanglement becomes the only distillable contribution to the entanglement. Employing a tensor network construction for gauge-invariant systems as defined by Zohar and Burrello we find that, in a vast range of cases, the leading term in the uperselection-resolved entanglement depends on the number of corners in the partition an unprecedently small corner-law (rather than area law) entanglement. The second example deals the steady state of noninteracting fermions, occupying a 1D lattice that hosts a generic scatterer at its center. It is coupled at its ends to two reservoirs biased by either voltage or temperature, leading to steady flows of the conserved particle number and energy. We show that disjoint intervals located on opposite sides of the scatterer, and within similar distances from it, maintain volume-law entanglement and total correlations regardless of their separation, as measured by their fermionic negativity and mutual information, respectively. Interestingly, this implies that if the position of one of the intervals is kept fixed, then the quantum correlation measures depend non-monotonically on the distance between the intervals. We derive exact analytical expressions for the extensive terms of these measures, which allow us to demonstrate that the strong long-range entanglement is generated by the coherence between the transmitted and reflected parts of propagating particles within the bias energy window. | |
| 16 | Sasha Mirlin | Karlsruhe Institute of Technology, Germany | Measurement-induced phase transitions in fermionic systems | We develop [1-5] a theory of measurement-induced phase transitions (MIPT) for d-dimensional lattice fermions subject to random measurements of local site occupation numbers. Our nalytical approach is based on Keldysh path-integral formalism and replica trick. For free fermions, we derive a non-linear sigma model (NLSM) as an effective field theory of the problem. Its replica-symmetric sector is a U(2)/U(1)xU(1) NLSM corresponding to observables linear in the density matrix; it describes diffusive behavior of average density fluctuations. The most interesting is the replica-asymmetric sector corresponding to observables that are non-linear in the density matrix. In particular, it describes propagation of quantum correlations of charge and of quantum information in a system. It is given by a (d+1)-dimensional isotropic NLSM defined of a chiral symmetry class AIII or BDI, with the target manifold SU(R) or SU(2R)/USp(2R), depending on presence of an additional effective time-reversal symmetry, with a replica limit R à 1. This establishes a close relation between MIPT and Anderson transitions. On the Gaussian level, the NLSM predicts diffusive behavior, implying that the entanglement entropy grows with system size as logarithm times area. However, the renormalization-group analysis shows that, for d=1, the "weak localization of information" develops asymptotically into strong localization, implying that the system is in the area-law phase even for a small measurement rate [1]. The corresponding localization length is however exponentially large for rare measurements. For d>1, we obtain a MIPT between the "diffusive" and "localized" phases of information and charge correlations [2]. The charge covariance G (linked to mutual information) in our theory is a counterpart of conductance in Anderson transitions. The "metallic" phase is characterized by "universal conductance fluctuations" of G and the critical point by scale-invariant distribution of G and by multifractality of two-point "conductance" [5]. Including interaction between fermions induce additional terms in the NLSM that affect the physics in a dramatic way [3]. First, this leads to the “information-charge separation”: charge cumulants get decoupled from entanglement entropies. Second, the interaction stabilizes the volume-law phase for the entanglement. Third, for spatial dimensionality d=1, the interaction stabilizes the phase with logarithmic growth of charge cumulants. We also explore a model of free fermions in d=1, subject to non-commuting local measurements across adjacent sites, which resolves the fermions into non-orthogonal orbitals, misaligned from the underlying lattice [4]. For maximal misalignment, superdiffusive behavior emerges from the vanishing of the measurement-induced quasiparticle decay rate at one point in the Brillouin zone, which generates fractal-scaling entanglement entropy S ∝ ℓ1/3 for a subsystem of length ℓ. We derive an effective NLSM with long-range couplings responsible for Lévy flights in entanglement propagation. When the misalignment is reduced, the entanglement exhibits, with increasing ℓ, consecutive regimes of superdiffusive, diffusive, and localized behavior. All analytical results are supported by numerical simulations [1-5]. [1] I. Poboiko, P. Pöpperl, I.V. Gornyi, A.D. Mirlin, Phys. Rev. X 13, 041046 (2023) [2] I. Poboiko, I.V. Gornyi, A.D. Mirlin, Phys. Rev. Lett. 132, 110403 (2024) [3] I. Poboiko, P. Pöpperl, I.V. Gornyi, A.D. Mirlin, Phys. Rev. B 111, 024204 (2025) [4] I. Poboiko, M. Szyniszewski, C.J. Turner, I.V. Gornyi, A.D. Mirlin, and A. Pal, arXiv:2501.12903 [5] I. Poboiko, I.V. Gornyi, A.D. Mirlin, in preparation |
| 17 | Dmitry Bagrets | |||
| 18 | Andreas Klumper | |||
| 19 | Tigran Sedrakyan | University of Massachusetts, Amherst | Unveiling chiral states in the XXZ chain | In this talk, I will present a detailed study of the low-energy properties of the one-dimensional spin-1/2 XXZ chain with time-reversal symmetry-breaking pseudo-scalar chiral interaction. I will propose a phase diagram for the model, focusing on the integrable case of the isotropic Heisenberg model with the chiral interaction. By employing the thermodynamic Bethe ansatz, I will discuss the concept of “chiralization”—the response of the ground state to the strength of the pseudo-scalar chiral interaction in a chiral Heisenberg chain. Notably, the chirality of the ground state remains zero until a critical coupling, α_c = (2/π)J, is reached, where J denotes the antiferromagnetic spin-exchange interaction. The two distinct phases, characterized by zero and finite chirality, are described by central-charge c = 1 conformal field theories (CFTs). Despite having identical central charges, I will argue that the difference between these emergent CFTs lies in the symmetry of their ground-state primary fields, leading to symmetry-enriched CFTs. Furthermore, at finite but small temperatures, the non-chiral Heisenberg phase acquires a finite chirality at finite but small temperatures that scales with the temperature quadratically. Finally, I will discuss how finite-size effects near the transition point provide a sensitive probe of the phase transition, offering insights into the underlying physics. |
| 20 | Sasha Gorsky | Phase-locking in dynamical systems and quantum mechanics | We discuss the relation between the dynamical system on the torus and the Hill equation, which is interpreted as either the equation of motion for the parametric oscillator or the Schr\"{o}dinger equation with periodic potential. The structure of phase-locking domains in the dynamical system on torus is mapped into the band-gap structure of the Hill equation. For the parametric oscillator, we provide the relation between non-adiabatic Hannay angle and the Poincar\'{e} rotation number of the corresponding dynamical system. In terms of quantum mechanics, the integer Poincar\'{e} rotation number is connected to the quantization number via the Milne's quantization approach and exact WKB. Using recent results concerning the exact WKB approach in quantum mechanics, we discuss the non-perturbative effects in the dynamical systems on the torus and for parametric oscillator. The semiclassical WKB is interpreted in the framework of a slow-fast dynamical system. The link between the classification of the coadjoint Virasoro orbits and the Hill equation yields a classification of the phase-locking domains in the parameter space in terms of the classification of Virasoro orbits. Our picture is supported by numerical simulations for the model of the Josephson junction and Mathieu equation. Joint paper with A. Alexandrov and A. Glutsyuk | |
| 21 | Nikolay Gromov | |||
| 22 | Leon Balents | Symmetry breaking patterns of 2+1d U(1) gauge theory with an SU(N) chemical potential and application to quantum antiferromagnets | We study the response of U(1) gauge theory on the lattice in 2+1 dimensions to an applied chemical potential coupling to a conserved SU(N) flavor charge. This mimics the physics of an applied Zeeman field coupling to a U(1) Dirac spin liquid. We observe several different symmetry breaking patterns and discuss the associated observable orders. We also investigate trial wavefunctions for antiferromagnets inspired by the gauge theory. | |
| 23 | Sergei Nechaev | |||
| 24 | Ferdinand Evers | Sample-to-sample fluctuations in many-body localization - a Fock-space perspective | The fate of localization in disordered quantum wires with short-range interactions, i.e., many-body localization (MBL), remains a subject of intense debate. While various scenarios have been proposed, no generally accepted theory has emerged so far. One particular issue that has received little to no attention in these scenarios is sample-to-sample fluctuations. We demonstrate that these fluctuations are enormous, especially in the regime of intermediate disorder strength—at least within the numerically accessible range of system sizes. Their origin becomes transparent within a Fock-space representation of system dynamics, naturally leading to a concept of “Fock-space connectivity,” which we introduce. Our analysis suggests that strong sample-to-sample fluctuations challenge the common notion that individual samples can be classified as either “localized” or “ergodic” based solely on the disorder strength parameter W, i.e., the variance of a sample’s disorder potential. Possible implications for MBL phase diagrams will be briefly discussed. (This work in progress is performed in close collaboration with S. Bera and his group at IITB.) | |
| 25 | Yuval Gefen | Effective linear response for non-equilibrium anyonic systems | The low-energy dynamics of two-dimensional topological matter hinges on its one-dimensional edge modes. Tunneling between fractional quantum Hall edge modes facilitates the study of anyonic statistics: it induces time-domain braiding that dominates signals from dilute anyon beams. We develop a framework for characterizing one-dimensional out-of-equilibrium anyonic states and define their effective chemical potential and temperature, both arising from anyonic braiding; these quantities depend on the effective (fractional) charge of the anyons and on their braiding phase. We further define electric and thermal transport coefficients in non-equilibrium anyonic setups. We show that in the extremely dilute limit, where contributions due to direct collisions of non-equilibrium anyons are negligible, the off-diagonal thermoelectric transport coefficients, i.e., Seebeck and Peltier coefficients, both vanish due to the symmetry between particle and hole distributions. This symmetry, however, is broken when deviating from this dilute limit. It follows that finite Seebeck and Peltier coefficients represent a smoking gun evidence of anyonic collisions. [1] Gu Zhang, Igor Gornyi, and Yuval Gefen, arXiv:2407.14203 and to be published. | |
| 26 | Felix von Oppen | |||
| 27 | Elio Koenig | Topologically enabled superconductivity and possible implications for rhombohedral graphene | We present a topological mechanism for superconductivity emerging from Chern-2 insulators. While, naively, time reversal symmetry breaking is expected to prevent superconductivity it turns out that the opposite is the case: An explicit model calculation for a generalized attractive-U Haldane-Hubbard model demonstrates that superconductivity is only stabilized near the quantum anomalous Hall state, but not near a trivial, time reversal symmetrical band insulator. We explain this using an effective fractionalized field theory involving fermionic chargeons, bosonic colorons and an emergent U(1) gauge field. When chargeons form a topological band structure, they prevent monopole proliferation ensuring a gapless photon. We argue that this photon should be interpreted as the Goldstone boson of the superfluid. Using random phase approximation on top of extensive slave-rotor mean-field calculations we characterize coherence length and stiffness of the superconductor. Thereby, we deduce the phase diagram in parameter space along with the universal nature of the superconducting transitions. We furthermore discuss the effect of doping and external magnetic field. We complement the fractionalized theory with calculations using an effective spin model and Gutzwiller projected wavefunctions. While mostly based on a simple toy model, we argue that our findings pave the way to a better understanding of superconductivity emerging out of spin- and valley polarized rhombohedral multilayer graphene in a parameter regime with nearby quantum anomalous Hall insulators. | |
| 28 | Nikita Nekrasov | |||
| 29 | Vladimir Kazakov | |||
| 30 | Victor Galitski | |||
| 31 | Boris Khesin | Univ. of Toronto, Canada | Geometry behind fluids | In 1966 V.Arnold suggested a group-theoretic approach to ideal hydrodynamics via the geodesic flow of the right-invariant energy metric on the group of volume-preserving diffeomorphisms of the flow domain. We describe several recent ramifications of this approach related to compressible fluids, optimal mass transport, as well as Newton's equations on diffeomorphism groups and smooth probability densities. It turns out that various important PDEs of hydrodynamical origin can be described in this geometric framework in a natural way. This is a joint work with G.Misiolek and K.Modin. |
| 32 | Gabriel Cardoso | |||
| 33 | Pavel Nosov | |||
| 34 | Rubik Poghossian | "A. I. Alikhanyan national science laboratory (Yerevan Physics Institute)" foundation | On 5-point conformal block with level 2 degenerate insertion and its AGT dual | In my talk I will present a new recursive method for studying the 5-point conformal Liouville block with degenerate level 2 insertion and its AGT dual. First, the solution of the BPZ differential equation satisfied by the conformal block is represented as a double series expansion. From the 2-node quiver gauge theory side, this expansion corresponds to the instanton series. It will be shown that the expansion coefficients are uniquely determined by a recursive relation. This series can be partially resummed, leading to an elegant expression in terms of a single hypergeometric function and its derivative. This new representation makes it straightforward to relate different asymptotic regions. As a by-product, we get a simple derivation of the fusion and braiding coefficients. It will be shown how a subtle procedure of merging the degenerate field with the outgoing state provides an alternative way of calculating the general 4-point block, which on the gauge theory side corresponds to the partition function of the SU(2) gauge theory with four massive hypermultiplets in the Omega background. These results are confirmed by comparison with known results obtained either from 2d conformal field theory or from the instanton count. |
| 35 | Alexander Zamolodchikov | |||
| 36 | Boris Svistunov | Transverse Quantum Superfluids | Even when ideal solids are insulating, their states with crystallographic defects may have superfluid properties. It became clear recently that edge dislocations in He-4 featuring a combination of microscopic quantum roughness and superfluidity of their cores may represent a new paradigmatic class of quasi-one-dimensional superfluids. The new state of matter, termed transverse quantum fluid (TQF), is found in a variety of physical setups. The key ingredient defining the class of TQF systems is infinite compressibility, which is responsible for all other unusual properties such as the quadratic spectrum of normal modes (or even the absence of sharp quasiparticles), irrelevance of the Landau criterion, off-diagonal long-range order at T = 0, and the exponential dependence of the phase slip probability on the inverse flow velocity. From a conceptual point of view, the TQF state is a striking demonstration of the conditional character of many dogmas associated with superfluidity, including the necessity of elementary excitations, in general, and the ones obeying the Landau criterion in particular. |