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Quantum friction between metals in the hydrodynamic regime Wu, Kunmin ; Schmidt, Thomas ; Farias, Maria Belen in Physical Review. A. (2022), 106 We study the phenomenon of quantum friction in a system consisting of a polarizable atom moving at a constant speed parallel to a metallic plate. The metal is described using a charged hydrodynamic model ... [more ▼] We study the phenomenon of quantum friction in a system consisting of a polarizable atom moving at a constant speed parallel to a metallic plate. The metal is described using a charged hydrodynamic model for the electrons. This model featuring long-range interactions is appropriate for a clean metal in a temperature range where scattering due to Coulomb interactions dominates over the scattering of electron by impurities. We find that a quantum friction force between the atom and the metal surface exists even in the absence of intrinsic damping in the metal, but that it only starts once the velocity of the atom exceeds the effective speed of sound in the metal. We argue that this condition can be fulfilled most easily in metals with nearly empty or nearly filled bands. We make quantitative predictions for the friction force to the second and fourth order in the atomic polarizability, and show that the threshold behavior persists to all orders of the perturbation theory. [less ▲] Detailed reference viewed: 55 (14 UL)Overlap of parafermionic zero modes at a finite distance ; Haller, Andreas ; et al in Physical Review Research (2022) Parafermion bound states (PBSs) are generalizations of Majorana bound states (MBSs) and have been predicted to exist as zero-energy eigenstates in proximitized fractional quantum Hall edge states ... [more ▼] Parafermion bound states (PBSs) are generalizations of Majorana bound states (MBSs) and have been predicted to exist as zero-energy eigenstates in proximitized fractional quantum Hall edge states. Similarly to MBSs, a finite distance between the PBS can split the ground state degeneracy. However, parafermionic modes have a richer exchange statistics than MBSs, so several interaction terms are allowed by the underlying $\mathbb{Z}_{2n}$ symmetry, rendering the effective Hamiltonian governing a pair of PBSs at a finite distance nontrivial. Here, we use a combination of analytical techniques (semiclassical instanton approximation) and numerical techniques (quantum Monte Carlo simulations) to determine the effective coupling Hamiltonian. For this purpose, we go beyond the dilute one-instanton gas approximation and show how finite-size effects can give rise to higher-order parafermion interactions. We find excellent agreement between the analytical results and Monte Carlo simulations. We estimate that these finite-size corrections should be observable in some of the recently proposed experiments to observe PBSs in strongly correlated systems. [less ▲] Detailed reference viewed: 29 (5 UL)Black hole mirages: electron lensing and Berry curvature effects in inhomogeneously tilted Weyl semimetals Haller, Andreas ; ; et al in arXiv (2022) We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a wide ... [more ▼] We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a wide regime of parameters, we show that electron flow is described well by semiclassical equations of motion similar to the ones governing gravitational attraction. This analogy provides a physically transparent tool for designing tiltronic devices, such as electronic lenses. The analogy to gravity circumvents the notoriously difficult full-fledged description of inhomogeneous solids, but a comparison to microscopic lattice simulations shows that it is only valid for trajectories sufficiently far from analogue black holes. We finally comment on the Berry curvature-driven transverse motion, and relate the latter to spin precession physics. [less ▲] Detailed reference viewed: 22 (4 UL)Current cross correlations in a quantum Hall collider at filling factor two Idrisov, Edvin ; ; et al in Physical Review. B, Condensed Matter (2022) Detailed reference viewed: 21 (1 UL)Supercurrent-enabled Andreev reflection in a chiral quantum Hall edge state ; ; et al E-print/Working paper (2022) Detailed reference viewed: 19 (3 UL)Kerr and Faraday rotations in topological flat and dispersive band structures ; ; et al in New Journal of Physics (2022), 24(6), 063003 Integer quantum Hall (IQH) states and quantum anomalous Hall (QAH) states show the same static dc response but distinct dynamical ac response. In particular, the ac anomalous Hall conductivity profile σ ... [more ▼] Integer quantum Hall (IQH) states and quantum anomalous Hall (QAH) states show the same static dc response but distinct dynamical ac response. In particular, the ac anomalous Hall conductivity profile σ yx (ω) is sensitive to the band shape of QAH states. For example, dispersive QAH bands shows resonance profile without a sign change at the band gap while the IQH states shows the sign change resonance at the cyclotron energy. We argue by flattening the dispersive QAH bands, σ yx (ω) should recover to that of flat Landau bands in IQH, thus it is necessary to know the origin of the sign change. Taking a topological lattice model with tunable bandwidth, we found that the origin of the sign change is not the band gap but the van Hove singularity energy of the QAH bands. In the limit of small bandwidth, the flat QAH bands recovers σ yx (ω) of the IQH Landau bands. Because of the Hall response, these topological bands exhibit giant polarization rotation and ellipticity in the reflected waves (Kerr effect) and rotation in the order of fine structure constant in the transmitted waves (Faraday effect) with profile resembles σ yx (ω). Our results serve as a simple guide to optical characterization for topological flat bands. [less ▲] Detailed reference viewed: 79 (2 UL)Coulomb drag of viscous electron fluids: drag viscosity and negative drag conductivity Hasdeo, Eddwi Hesky ; ; Schmidt, Thomas E-print/Working paper (2022) Detailed reference viewed: 19 (0 UL)Quantum Skyrmion Lattices in Heisenberg Ferromagnets Haller, Andreas ; ; et al E-print/Working paper (2021) Skyrmions are topological magnetic textures which can arise in non-centrosymmetric ferromagnetic materials. In most systems experimentally investigated to date, skyrmions emerge as classical objects ... [more ▼] Skyrmions are topological magnetic textures which can arise in non-centrosymmetric ferromagnetic materials. In most systems experimentally investigated to date, skyrmions emerge as classical objects. However, the discovery of skyrmions with nanometer length scales has sparked interest in their quantum properties. Quantum corrections to the classical magnetic textures have already been considered in the semiclassical regime. Here, we go beyond this limit by investigating quantum skyrmions in the deep quantum regime. We use density matrix renormalization group techniques to study two-dimensional spin-1/2 Heisenberg ferromagnets with Dzyaloshinskii-Moriya interactions and discover a broad region in the zero temperature phase diagram which hosts quantum skyrmion lattice ground states. We argue that this novel quantum skyrmion phase can be detected experimentally in the magnetization profile via local magnetic polarization measurements as well as in the spin structure factor measurable via neutron scattering experiments. Finally, we explore the resulting quantum skyrmion state, analyze its real space polarization profile and show that it is a non-classical state featuring entanglement between quasiparticle and environment mainly localized near the boundary spins of the skyrmion. [less ▲] Detailed reference viewed: 49 (10 UL)In-plane magnetic field-driven symmetry breaking in topological insulator-based three-terminal junctions ; ; et al in Communications Materials (2021) Topological surface states of three-dimensional topological insulator nanoribbons and their distinct magnetoconductance properties are promising for topoelectronic applications and topological quantum ... [more ▼] Topological surface states of three-dimensional topological insulator nanoribbons and their distinct magnetoconductance properties are promising for topoelectronic applications and topological quantum computation. A crucial building block for nanoribbon-based circuits are three-terminal junctions. While the transport of topological surface states on a planar boundary is not directly affected by an in-plane magnetic field, the orbital effect cannot be neglected when the surface states are confined to the boundary of a nanoribbon geometry. Here, we report on the magnetotransport properties of such three-terminal junctions. We observe a dependence of the current on the in-plane magnetic field, with a distinct steering pattern of the surface state current towards a preferred output terminal for different magnetic field orientations. We demonstrate that this steering effect originates from the orbital effect, trapping the phase-coherent surface states in the different legs of the junction on opposite sides of the nanoribbon and breaking the left-right symmetry of the transmission across the junction. The reported magnetotransport properties demonstrate that an in-plane magnetic field is not only relevant but also very useful for the characterization and manipulation of transport in three-dimensional topological insulator nanoribbon-based junctions and circuits, acting as a topoelectric current switch. [less ▲] Detailed reference viewed: 37 (1 UL)Artificial event horizons in Weyl semimetal heterostructures and their non-equilibrium signatures De Beule, Christophe ; Groenendijk, Solofo ; et al in SciPost Physics (2021), 11 Detailed reference viewed: 51 (2 UL)Kerr effect in tilted nodal loop semimetals Ekström, Carl Johan Ingvar ; Hasdeo, Eddwi Hesky ; Farias, Maria Belen et al in Physical Review. B (2021), 104(12), 125411 We investigate the optical activity of tilted nodal loop semimetals. We calculate the full conductivity matrix for a band structure containing a nodal loop with possible tilt in the x−y plane, which ... [more ▼] We investigate the optical activity of tilted nodal loop semimetals. We calculate the full conductivity matrix for a band structure containing a nodal loop with possible tilt in the x−y plane, which allows us to study the Kerr rotation and ellipticity both for a thin film and a bulk material. We find signatures in the Kerr signal that give direct information about the tilt velocity and direction, the radius of the nodal loop and the internal chemical potential of the system. These findings should serve as guide to understanding optical measurements of nodal loop semimetals and as an additional tool to characterize them. [less ▲] Detailed reference viewed: 80 (7 UL)Generalized Chern numbers based on open system Green's functions Farias, Maria Belen ; ; Schmidt, Thomas in New Journal of Physics (2021), 23 We present an alternative approach to studying topology in open quantum systems, relying directly on Green's functions and avoiding the need to construct an effective non-Hermitian (nH) Hamiltonian. We ... [more ▼] We present an alternative approach to studying topology in open quantum systems, relying directly on Green's functions and avoiding the need to construct an effective non-Hermitian (nH) Hamiltonian. We define an energy-dependent Chern number based on the eigenstates of the inverse Green's function matrix of the system which contains, within the self-energy, all the information about the influence of the environment, interactions, gain or losses. We explicitly calculate this topological invariant for a system consisting of a single 2D Dirac cone and find that it is half-integer quantized when certain assumptions about the self-energy are made. Away from these conditions, which cannot or are not usually considered within the formalism of nH Hamiltonians, we find that such a quantization is usually lost and the Chern number vanishes, and that in special cases, it can change to integer quantization. [less ▲] Detailed reference viewed: 48 (5 UL)Universal Hall conductance scaling in non-Hermitian Chern insulators ; Schmidt, Thomas ; in Physical Review Research (2021) We investigate the Hall conductance of a two-dimensional Chern insulator coupled to an environment causing gain and loss. Introducing a biorthogonal linear response theory, we show that sufficiently ... [more ▼] We investigate the Hall conductance of a two-dimensional Chern insulator coupled to an environment causing gain and loss. Introducing a biorthogonal linear response theory, we show that sufficiently strong gain and loss lead to a characteristic nonanalytical contribution to the Hall conductance. Near its onset, this contribution exhibits a universal power law with a power 3/2 as a function of Dirac mass, chemical potential, and gain strength. Our results pave the way for the study of non-Hermitian topology in fermionic transport experiments. [less ▲] Detailed reference viewed: 29 (0 UL)Electron hydrodynamics of anomalous Hall materials Hasdeo, Eddwi Hesky ; Ekström, Carl Johan Ingvar ; Idrisov, Edvin et al in Physical Review. B (2021), 103(12), 125106 We study two-dimensional electron systems in the hydrodynamic regime. We show that a geometrical Berry curvature modifies the effective Navier-Stokes equation for viscous electron flow in topological ... [more ▼] We study two-dimensional electron systems in the hydrodynamic regime. We show that a geometrical Berry curvature modifies the effective Navier-Stokes equation for viscous electron flow in topological materials. For small electric fields, the Hall current becomes negligible compared to the viscous longitudinal current. In this regime, we highlight an unconventional Poiseuille flow with an asymmetric profile and a deviation of the maximum of the current from the center of the system. In a two-dimensional infinite geometry, the Berry curvature leads to current whirlpools and an asymmetry of potential profile. This phenomenon can be probed by measuring the asymmetric non-local resistance profile. [less ▲] Detailed reference viewed: 105 (17 UL)Optical properties of topological flat and dispersive bands Habibi, Alireza ; ; et al E-print/Working paper (2021) We study the optical properties of topological flat and dispersive bands. Due to their topological nature, there exists an anomalous Hall response which gives rise to a transverse current without applied ... [more ▼] We study the optical properties of topological flat and dispersive bands. Due to their topological nature, there exists an anomalous Hall response which gives rise to a transverse current without applied magnetic field. The dynamical Hall conductivity of systems with flat bands exhibits a sign change when the excitation energy is on resonance with the band gap, similar to the magnetotransport Hall conductivity profile. The sign change of the Hall conductivity is located at the frequency corresponding to the singularity of the joint density of states, i.e., the van Hove singularity (VHS). For perfectly flat bands, this VHS energy matches the band gap. On the other hand, in the case of dispersive bands, the VHS energy is located above the band gap. As a result, the two features of the Hall conductivity, i.e., the resonant feature at the band gap and the sign change at the VHS energy, become separated. This anomalous Hall response rotates the polarization of an electric field and can be detected in the reflected and transmitted waves, as Kerr and Faraday rotations, respectively, thus allowing a simple optical characterization of topological flat bands. [less ▲] Detailed reference viewed: 61 (9 UL)Heat transport in overdamped quantum systems ; Schmidt, Thomas ; Esposito, Massimiliano et al in Physical Review. B (2020), 102 Detailed reference viewed: 168 (23 UL)In-plane magnetic field-driven symmetry breaking in topological insulator-based three-terminal junctions ; ; Schmidt, Thomas et al E-print/Working paper (2020) Detailed reference viewed: 38 (0 UL)Current correlations of Cooper-pair tunneling into a quantum Hall system Michelsen, Andreas Nicolai Bock ; Schmidt, Thomas ; Idrisov, Edvin in Physical Review. B, Condensed Matter and Materials Physics (2020), 102 Detailed reference viewed: 66 (4 UL)Casimir force between Weyl semimetals in a chiral medium Farias, Maria Belen ; ; Schmidt, Thomas in Physical Review. B (2020), 101 Detailed reference viewed: 70 (5 UL)Transport properties of coupled Majorana bound states in the Coulomb blockade regime Ekström, Carl Johan Ingvar ; ; Schmidt, Thomas in Physical Review. B, Condensed Matter and Materials Physics (2020) Topologically protected qubits based on nanostructures hosting Majorana bound states (MBSs) hold great promise for fault-tolerant quantum computing. We study the transport properties of nanowire networks ... [more ▼] Topologically protected qubits based on nanostructures hosting Majorana bound states (MBSs) hold great promise for fault-tolerant quantum computing. We study the transport properties of nanowire networks hosting MBSs with a focus on the effects of the charging energy and the overlap between neighboring MBSs in short mesoscopic samples. In particular, we investigate structures hosting four MBSs such as T junctions and Majorana boxes. Using a master equation in the Markovian approximation, we discuss the leading transport processes mediated by the MBSs. Single-electron tunneling and processes involving creation and annihilation of Cooper pairs dominate in the sequential-tunneling limit. In the cotunneling regime the charge in the MBSs is fixed and transport is governed by transitions via virtual intermediate states. Our results show that four-terminal measurements in the T junction and Majorana box geometries can be useful tools for the characterization of the properties of MBSs with finite overlaps and charging energy. [less ▲] Detailed reference viewed: 97 (9 UL) |
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