arXiv subjects

A. L. Chudnovskiy

Publications and source records attributed to A. L. Chudnovskiy.

At least 19 recordsLinked to original sources

arXiv2025

Coulomb drag by motion of a monolayer polar crystal through graphene nanoconstriction

We theoretically predict that the motion of a polar crystalline layer between two graphene planes exerts Coulomb drag on electrons in graphene, inducing a DC drag current. The physical mechanism underlying this drag arises from intervalley scattering of charge carriers in graphene caused by the time-dependent potential of the moving crystalline layer. This drag effect manifests above a finite threshold doping of the graphene layers, which is determined by the lattice structure and the relative orientation of the crystalline layer with respect to the graphene lattice. Additionally, the drag current exhibits a nonlinear Hall effect due to the interplay between the induced nonequilibrium pseudospin and the intrinsic pseudospin-orbit coupling in graphene. In turn, the drag exerted on electrons in graphene produces a backaction on the crystalline layer, which can be described as an increase in its dynamic viscosity.

cond-mat.mes-hall↗

arXiv2023

Coulomb drag and heat transfer in strange metals

We address Coulomb drag and near-field heat transfer in a double-layer system of incoherent metals. Each layer is modeled by an array of tunnel-coupled SYK dots with random inter-layer interactions. Depending on the strength of intra-dot interactions and inter-dot tunneling, this model captures the crossover from the Fermi liquid to a strange metal phase. The absence of quasiparticles in the strange metal leads to temperature-independent drag resistivity, which is in strong contrast with the quadratic temperature dependence in the Fermi liquid regime. We show that all the parameters can be independently measured in near-field heat transfer experiments, performed in Fermi liquid and strange metal regimes.

cond-mat.str-el↗

arXiv2022

Superconductor--Insulator Transition in a non-Fermi Liquid

We present a model of a strongly correlated system with a non-Fermi liquid high temperature phase. Its ground state undergoes an insulator to superconductor quantum phase transition (QPT) as a function of a pairing interaction strength. Both the insulator and the superconductor are originating from the same interaction mechanism. The resistivity in the insulating phase exhibits the activation behavior with the activation energy, which goes to zero at the QPT. This leads to a wide quantum critical regime with an algebraic temperature dependence of the resistivity. Upon raising the temperature in the superconducting phase, the model exhibits a finite temperature phase transition to a Bose metal phase, which separates the superconductor from the non-Fermi liquid metal.

cond-mat.str-el↗

arXiv2020

SYK Superconductivity: Quantum Kuramoto and Generalized Richardson Models

Sachdev-Ye-Kitaev (SYK) model has emerged as a new paradigm of the non-Fermi-liquid behavior. Here we investigate a possibility of having a superconducting off-diagonal long-range order (ODLRO) and a pseudogap phase within the SYK framework. We found that ODLRO may be established in spin-1/2 version of the model with the time-reversal invariance and an extra attractive interaction. If the latter is taken as the on-site negative-$U$ Hubbard term, it leads to the pseudogap phase at $U<U_c$ dominated by quantum fluctuations of local phases. These fluctuations are described by a quantum version of the Kuramoto model, traditionally employed to illustrate synchronization of classical non-linear oscillators. In the opposite limit of large $U$, the SYK+Hubbard model is approaching a certain generalization of the integrable Richardson model. We present exact diagonalization studies, along with analytic solutions of the aforementioned limiting cases. We also discuss possible holographic interpretations of the model, ODLRO and the pseudogap.

cond-mat.str-el↗

arXiv2018

On the replica structure of Sachdev-Ye-Kitaev model

We investigate existence of replica off-diagonal solutions in the field-theoretical description of Sachdev-Ye-Kitaev model. To this end we evaluate a set of local and non-local dynamic correlation functions in the long time limit. We argue that the structure of the soft-mode Schwarzian action is qualitatively different in replica-diagonal vs. replica-off-diagonal scenarios, leading to distinct long-time predictions for the correlation functions. We then evaluate the corresponding correlation functions numerically and compare the simulations with analytical predictions of replica-diagonal and replica-off-diagonal calculations. We conclude that all our numerical results are in a quantitative agreement with the theory based on the replica-diagonal saddle point plus Schwarzian and massive Gaussian fluctuations (the latter do contain replica off-diagonal components). This seems to exclude any contributions from replica-off-diagonal saddle points, at least on the time scales shorter than the inverse many-body level spacing.

hep-th↗

arXiv2018

Symmetry-restoring quantum phase transition in a two-dimensional spinor condensate

Bose Einstein condensates of spin-1 atoms are known to exist in two different phases, both having spontaneously broken spin-rotation symmetry, a ferromagnetic and a polar condensate. Here we show that in two spatial dimensions it is possible to achieve a quantum phase transition from a polar condensate into a singlet phase symmetric under rotations in spin space. This can be done by using particle density as a tuning parameter. Starting from the polar phase at high density the system can be tuned into a strong-coupling intermediate-density point where the phase transition into a symmetric phase takes place. By further reducing the particle density the symmetric phase can be continuously deformed into a Bose-Einstein condensate of singlet atomic pairs. We calculate the region of the parameter space where such a molecular phase is stable against collapse.

cond-mat.quant-gas↗

arXiv2018

Stability of a topological insulator: interactions, disorder and parity of Kramers doublets

We study stability of multiple conducting edge states in a topological insulator against all multi-particle perturbations allowed by the time-reversal symmetry. We model a system as a multi-channel Luttinger liquid, where the number of channels equals the number of Kramers doublets at the edge. We show that in the clean system with N Kramers doublets there always exist relevant perturbations (either of superconducting or charge density wave character) which always open (N-1) gaps. In the charge density wave regime, (N-1) edge states get localised. The single remaining gapless mode describes sliding of 'Wigner crystal' like structure. Disorder introduces multi-particle backscattering processes. While the single-particle backscattering turns out to be irrelevant, the two-particle process may localise this gapless, in translation invariant system, mode. Our main result is that an interacting system with N Kramers doublets at the edge may be either a trivial insulator or a topological insulator for N=1 or 2, depending on density-density repulsion parameters whereas any higher number N>2 of doublets gets fully localised by the disorder pinning irrespective of the parity issue.

cond-mat.str-el↗

arXiv2017

Metal-insulator transition in a sliding Luttinger liquid with line defects

We investigate the effect of both strong and weak potential scattering caused by local impurities and extended (line) defects in the array of Luttinger liquid wires. We find that in both cases a finite range inter-wire interaction stabilises metallic state. Based on calculation of the scaling dimensions of one-particle scattering operators, we construct the phase diagram for low-temperature transport along the array. We find that unlike local impurity case where only conducting and insulating states are realised (metal-insulator transition driven by interactions), the extended line defects may bring the system into a mixed state where conducting or insulating behavior can be observed depending on bare strength of the scatterer (metal-insulator transition driven by disorder).

cond-mat.str-el↗

arXiv2017

Microwave control of coupling parameters in spinor alkali condensates

We propose a protocol which utilises radio frequency magnetic pulses in order to tune the effective two-particle scattering amplitudes for alkali atoms in the $F=1$ hyperfine ground state. Unlike the Feshbach resonance method, the proposed protocol preserves with controllable accuracy the global rotational symmetry in the spin space offering access to a broad region of the phase diagram of the rotationally-symmetric spinor Bose condensate. Examples of $^{41}$K and $^{7}$Li are considered and it is shown that for these atoms sufficient variation in the effective coupling constants can be achieved in order to explore phase transitions between different symmetry-broken phases of the condensate.

cond-mat.quant-gas↗

arXiv2015

Thermal and electrical quantum Hall effects in ferromagnet-topological insulator-ferromagnet junction

We present the theoretical description for a class of experimental setups that measure quantum Hall coefficients in ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junctions. We predict that varying the magnetization direction in ferromagnets, one can change the induced Hall voltage and transverse temperature gradient from the maximal values, corresponding to the quantized Hall coefficients, down to their complete suppression to zero. We provide detailed analysis of thermal and electrical Hall resistances as functions of the magnetization directions in ferromagnets, the spin-scattering time in TI, and geometrical positions of FM leads and measurement contacts.

cond-mat.mes-hall↗

arXiv2014

Topological insulator in junction with ferromagnets: quantum Hall effects

The ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction exhibits thermal and electrical quantum Hall effects. The generated Hall voltage and transverse temperature gradient can be controlled by the directions of magnetizations in the FM leads, which inspires the use of FM-TI-FM junctions as electrical and as heat switches in spintronic devices. Thermal and electrical Hall coefficients are calculated as functions of the magnetization directions in ferromagnets and the spin-relaxation time in TI. Both the Hall voltage and the transverse temperature gradient decrease but are not completely suppressed even at very short spin-relaxation times. The Hall coefficients turn out to be independent of the spin-relaxation time for symmetric configuration of FM leads.

cond-mat.mes-hall↗

arXiv2013

Decoherence induced by magnetic impurities in quantum Hall system

Scattering by magnetic impurities is known to destroy coherence of electron motion in metals and semiconductors. We investigate the decoherence introduced in a single act of electron scattering by a magnetic impurity in a quantum Hall system. To this end we introduce a fictitious nonunitary scattering matrix $\mathcal{S}$ for electrons that reproduces the exactly calculated scattering probabilities. The strength of decoherence is identified by the deviation of eigenvalues of the product $\mathcal{S}\mathcal{S}^{\dagger}$ from unity. Using the fictitious scattering matrix, we estimate the width of the metallic region at the quantum Hall effect inter-plateau transition and its dependence on the exchange coupling strength and the degree of polarization of magnetic impurities.

cond-mat.mes-hall↗

arXiv2011

Dynamics of nano-magnetic oscillators

We explore how non-equilibrium noise affects spin-torque switching elements and oscillators. To do so we first discuss the deterministic dynamics of magnetic tunnel junctions, introducing a convenient set of slow and fast degrees of freedom. We then derive effective Langevin equation for the slowly varying energy of precessional orbit and introduce the corresponding energy noise and energy diffusion coefficient. This allows for the formulation of a Fokker-Planck equation for the energy density distribution. We use it to analyse switching time distribution as well as the shape of the optimal spin-current pulse, which minimizes Joule losses of a switch. Finally we derive a generic expression for the linewidth of a spin-torque oscillator and discuss its dependence on temperature, spin-current amplitude and other parameters.

cond-mat.mes-hall↗

arXiv2011

Doublon relaxation in the Bose-Hubbard model

Decay of a high-energy double occupancy state, doublon, in a narrow-band lattice requires creation of a coherent many-particle excitation. This leads to an exponentially long relaxation time of such a state. We show that, if the average occupation number is sufficiently small, the corresponding exponent may be evaluated exactly. To this end we develop the quasiclassical approach to calculation of the high-order tree-level decay amplitudes.

cond-mat.quant-gas↗

arXiv2009

Spin-flip scattering at quantum Hall transition

We formulate a generalized Chalker--Coddington network model that describes the effect of nuclear spins on the two-dimensional electron gas in the quantum Hall regime. We find exact analytical expression for the transmission coefficient of a charged particle through a saddle point potential in presence of perpendicular magnetic field that takes into account spin-flip processes. Spin-flip scattering creates a metallic state in a finite range around the critical energy of quantum Hall transition. As a result we find that the usual insulating phases with Hall conductance $σ_{xy}=0, 1, 2$ are separated by novel metallic phases.

cond-mat.dis-nn↗

arXiv2009

Kondo effect and RKKY interaction in magnetic trimers

Clusters of magnetic atoms lying on a metallic substrate can exhibit Kondo effect due to the exchange interaction with mobile electrons in the metal, which can be observed in STM measurements. The same interaction results in the induced RKKY interaction between the magnetic moments in the cluster. For different geometries of the cluster, it can enhance or suppress Kondo-correlations. We calculate the tunneling density of states for trimer clusters of different geometries and reveal the signatures of competition between the Kondo effect and RKKY interaction that can be seen in STM experiments.

cond-mat.str-el↗

arXiv2008

Double quantum dot as a probe of nonequilibrium charge fluctuations at the quantum point contact

Absorption of energy quanta generated by quantum point contact results in the inelastic current through the double quantum dot placed nearby. In contrast to a single quantum dot, the inelastic current through the double quantum dot is sensitive to the energy dependence of the quantum point contact transmission, which can explain the experimentally observed features. We calculate the inelastic current as a function of microscopic parameters of the circuit.

cond-mat.mes-hall↗

arXiv2008

Spin-torque shot noise in magnetic tunnel junctions

Spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spin-torque phenomenon. At the same time the shot noise, associated with the current, leads to a non-equilibrium stochastic force acting on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert equation for a magnetization of a ''free'' ferromagnetic layer in contact with a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and show that the non-equilibrium noise yields to a non-monotonous dependence of the precession spectrum linewidth on the current.

cond-mat.mes-hall↗