Publications

Order by: publication date number of citations

• Topological insulators and geometry of vector bundles

  Alexander S. Sergeev

  SciPost Phys. Lect. Notes 67 (2023) · published 12 April 2023 | Toggle abstract · pdf

  For a long time, band theory of solids has focused on the energy spectrum, or Hamiltonian eigenvalues. Recently, it was realized that the collection of eigenvectors also contains important physical information. The local geometry of eigenspaces determines the electric polarization, while their global twisting gives rise to the metallic surface states in topological insulators. These phenomena are central topics of the present notes. The shape of eigenspaces is also responsible for many intriguing physical analogies, which have their roots in the theory of vector bundles. We give an informal introduction to the geometry and topology of vector bundles and describe various physical models from this mathematical perspective.

  1 citation

• Gate-defined Kondo lattices with valley-helical quantum dot arrays

  Antonio L. R. Manesco

  SciPost Phys. 19, 024 (2025) · published 18 July 2025 | Toggle abstract · pdf

  Kondo physics and heavy-fermion behavior has been predicted and observed in moiré materials. The electric tunability of moiré materials allows an in-situ study of Kondo lattices' phase diagrams, which is not possible with their intermetallic counterparts. However, moiré platforms rely on twisting, which introduces twisting angle disorder and undesired buckling. Here we propose device layouts for one- and two-dimensional gate-defined superlattices in Bernal bilayer graphene where localized states couple to dispersive valley-helical modes. We show that, under electronic interactions, these superlattices are described by an electrically-tunable Kondo-Heisenberg model.

  1 citation

• Entropic analysis of optomechanical entanglement for a nanomechanical resonator coupled to an optical cavity field

  Jeong Ryeol Choi

  SciPost Phys. Core 4, 024 (2021) · published 20 September 2021 | Toggle abstract · pdf

  We investigate entanglement dynamics for a nanomechanical resonator coupled to an optical cavity field through the analysis of the associated entanglement entropies. The effects of time variation of several parameters, such as the optical frequency and the coupling strength, on the evolution of entanglement entropies are analyzed. We consider three kinds of entanglement entropies as the measures of the entanglement of subsystems, which are the linear entropy, the von Neumann entropy, and the Renyi entropy. The analytic formulae of these entropies are derived in a rigorous way using wave functions of the system. In particular, we focus on time behaviors of entanglement entropies in the case where the optical frequency is modulated by a small oscillating factor. We show that the entanglement entropies emerge and increase as the coupling strength grows from zero. The entanglement entropies fluctuate depending on the adiabatic variation of the parameters and such fluctuations are significant especially in the strong coupling regime. Our research may deepen the understanding of the optomechanical entanglement, which is crucial in realizing hybrid quantum-information protocols in quantum computation, quantum networks, and other domains in quantum science.

  1 citation

• 2d dualities from 4d

  Jiaqun Jiang, Satoshi Nawata, Jiahao Zheng

  SciPost Phys. 18, 180 (2025) · published 6 June 2025 | Toggle abstract · pdf

  We find new $\mathcal{N}=(2,2)$ and $\mathcal{N}=(0,2)$ dualities through the twisted compactifications of 4d supersymmetric theories on $S^2$. Our findings include dualities for both $\mathcal{N}=(2,2)$ and $\mathcal{N}=(0,2)$ non-Abelian gauge theories, as well as $\mathcal{N}=(0,2)$ Gauge/Landau-Ginzburg duality.

  1 citation

• Quantum circuit simulation of linear optics using fermion to qubit encoding

  Seungbeom Chin, Jaehee Kim, Joonsuk Huh

  SciPost Phys. Core 7, 042 (2024) · published 15 July 2024 | Toggle abstract · pdf

  This work proposes a digital quantum simulation protocol for the linear scattering process of bosons, which provides a simple extension to partially distinguishable boson cases. Our protocol is achieved by combining the boson-fermion correspondence relation and fermion to qubit encoding protocols. As a proof of concept, we designed quantum circuits for generating the Hong-Ou-Mandel dip by varying particle distinguishability. The circuits were verified with the classical and quantum simulations using the IBM Quantum and IonQ cloud services.

  1 citation

• Bloch-Lorentz magnetoresistance oscillations in delafossites

  Kostas Vilkelis, Lin Wang, Anton Akhmerov

  SciPost Phys. 15, 019 (2023) · published 20 July 2023 | Toggle abstract · pdf

  Recent measurements of the out-of-plane magnetoresistance of delafossites (PdCoO$_2$ and PtCoO$_2$) observed oscillations closely resembling the Aharonov-Bohm effect. Here, we show that the magnetoresistance oscillations are explained by the Bloch-like oscillations of the out-of-plane electron trajectories. We develop a semiclassical theory of these Bloch-Lorentz oscillations and show that they are a consequence of the ballistic motion and quasi-2D dispersion of delafossites. Our model identifies the sample wall scattering to be the most likely factor limiting the visibility of these Bloch-Lorentz oscillations in existing experiments.

  1 citation

• Stress correlations in near-crystalline packings

  Roshan Maharana, Kabir Ramola

  SciPost Phys. 17, 012 (2024) · published 15 July 2024 | Toggle abstract · pdf

  We derive exact results for stress correlations in near-crystalline systems in two and three dimensions. We study energy minimized configurations of particles interacting through Harmonic as well as Lennard-Jones potentials, for varying degrees of microscopic disorder and quenched forces on grains. Our findings demonstrate that the macroscopic elastic properties of such near-crystalline packings remain unchanged within a certain disorder threshold, yet they can be influenced by various factors, including packing density, pressure, and the strength of inter-particle interactions. We show that the stress correlations in such systems display anisotropic behavior at large lengthscales and are significantly influenced by the pre-stress of the system. The anisotropic nature of these correlations remains unaffected as we increase the strength of the disorder. Additionally, we derive the large lengthscale behavior for the change in the local stress components that shows a $1/r^d$ radial decay for the case of particle size disorder and a $1/r^{d-1}$ behavior for quenched forces introduced into a crystalline network. Finally, we verify our theoretical results numerically using energy-minimised static particle configurations.

  1 citation

• Mapping a dissipative quantum spin chain onto a generalized Coulomb gas

  Oscar Bouverot-Dupuis

  SciPost Phys. 17, 130 (2024) · published 11 November 2024 | Toggle abstract · pdf

  An XXZ spin chain at zero magnetization is subject to spatially correlated baths acting as dissipation. We show that the low-energy excitations of this model are described by a dissipative sine-Gordon field theory, i.e. a sine-Gordon action with an additional long-range interaction emerging from dissipation. The field theory is then exactly mapped onto a generalized Coulomb gas which, in addition to the usual integer charges, displays half-integer charges that originate from the dissipative baths. These new charges come in pairs linked by a charge independent logarithmic interaction. In the Coulomb gas picture, we identify a Berezinsky–Kosterlitz–Thouless-like phase transition corresponding to the binding of charges and derive the associated perturbative renormalization group equations. For superohmic baths, the transition is due to the binding of the integer charges, while for subohmic baths, it is due to the binding of the half-integer charges, thereby signaling a dissipation-induced transition.

  1 citation

• Topological interface states - A possible path towards a Landau-level laser in the THz regime

  Mark Oliver Goerbig

  SciPost Phys. 15, 246 (2023) · published 19 December 2023 | Toggle abstract · pdf

  Volkov-Pankratov surface bands arise in smooth topological interfaces, i.e. interfaces between a topological and a trivial insulator, in addition to the chiral surface state imposed by the bulk-surface correspondence of topological materials. These two-dimensional bands become Landau-quantized if a magnetic field is applied perpendicular to the interface. I show that the energy scales, which are typically in the 10-100 meV range, can be controlled both by the perpendicular magnetic field and the interface width. The latter can still be varied with the help of a magnetic-field component in the interface. The Landau levels of the different Volkov-Pankratov bands are optically coupled, and their arrangement may allow one to obtain population inversion by optical pumping. This could serve as the elementary brick of a multi-level laser based on Landau levels. Moreover, the photons are absorbed and emitted either parallel or perpendicular to the magnetic field, respectively in the Voigt and Faraday geometry, depending on the Volkov-Pankratov bands and Landau levels involved in the optical transitions.

  1 citation

• On perturbation around closed exclusion processes

  Masataka Watanabe

  SciPost Phys. 17, 092 (2024) · published 25 September 2024 | Toggle abstract · pdf

  We derive the formula for the stationary states of particle-number conserving exclusion processes infinitesimally perturbed by inhomogeneous adsorption and desorption. The formula not only proves but also generalises the conjecture proposed in [Phys. Rev. E 97, 032135] to account for inhomogeneous adsorption and desorption. As an application of the formula, we draw part of the phase diagrams of the open asymmetric simple exclusion process with and without Langmuir kinetics, correctly reproducing known results.

  1 citation