arXiv subjects

E. G. Mishchenko

Publications and source records attributed to E. G. Mishchenko.

At least 19 recordsLinked to original sources

arXiv2026

Anomaly-Induced Hybrid Bulk Electromagnetic Mode in Weyl Semimetals

Collective modes provide direct fingerprints of quantum matter. We predict a previously unidentified hybrid bulk electromagnetic mode in Weyl semimetals arising from the interplay between the chiral anomaly and the orientation of its associated chiral magnetic response relative to the direction of the wave-vector. When the anomaly-induced chiral magnetic current has a component along the propagation direction, oscillations of valley imbalance hybridize with plasmonic charge oscillations, producing a linearly dispersing mode that undergoes avoided crossing with the bulk plasmon, producing a hybrid bulk excitation absent in ordinary metals. The hybrid mode provides a direct signature of Weyl semimetals and a probe of the chiral anomaly and its associated chiral magnetic effect, with observable features in electron energy-loss spectroscopy. Studying this interplay can uncover various optical and electronic properties of Weyl semimetals.

cond-mat.mes-hall↗

arXiv2024

Lattice deformation induced by hot carriers in graphene

Hot electrons formed in a graphene crystal by high-intensity short-duration laser pulses can exist for a time that is less than an electron-phonon energy relaxation time. During that time, electron-electron collisions cause the electrons to thermalize to a local effective temperature that propagates (diffuses) through graphene. The non-uniform nature of the electron temperature leads to a force acting on the graphene lattice. This force is the result of the electron-lattice interaction that exists even at times that are less than the electron-phonon scattering time. The force causes the lattice to deform. A Boltzmann equation description of the transient electron-lattice deformation causes by hot electrons in graphene is presented.

cond-mat.mes-hall↗

arXiv2023

Collective spin oscillations in a magnetized graphene sheet

We investigate collective spin excitations of graphene electrons with short-ranged interactions and subject to the external Zeeman magnetic field. We find that in addition to the familiar Silin spin wave, a collective spin-flip excitation that reduces to the uniform precession when the wave's momentum approaches zero, the magnetized graphene supports another collective mode visible in the transverse spin susceptibility: a collective spin-current mode. Unlike the Silin wave, this mode is not dictated by the spin-rotational symmetry but rather owns its existence to the pseudo-spin structure of the graphene lattice. We find the new collective excitation to become sharply defined in a finite interval of wave's momenta, the range of which is determined by the interaction and the magnetization.

cond-mat.mes-hall↗

arXiv2020

Dynamic response functions of two-dimensional Dirac fermions with screened Coulomb and short-range interactions

We consider a screened Coulomb interaction between electrons in graphene and determine their dynamic response functions, such as a longitudinal and a transverse electric conductivity and a polarization function and compare them to the corresponding quantities in the short-range interaction model. The calculations are performed to all orders for short-range interaction by taking into account the self-energy renormalization of the electron velocity and using a ladder approximation to account for the vertex corrections, ensuring that the Ward identity (charge conservation law) is satisfied. Our findings predict a resonant response of interacting electron-hole pairs at a particular frequency below the threshold $qv=ω$ and further predict an instability for sufficiently strong interactions.

cond-mat.mes-hall↗

arXiv2019

Enhanced interaction effects in the vicinity of the topological transition

A metal near the topological transition can be loosely viewed as consisting of two groups of electrons. First group are "bulk" electrons occupying most of the Brillouin zone. Second group are electrons with wave vectors close to the topological transition point. Kinetic energy, $\tilde{E}_F$, of electrons of the first group is much bigger than kinetic energy, $E_F$, of electrons of the second group. With electrons of the second group being slow, the interaction effects are more pronounced for these electrons. We perform a calculation illustrating that electrons of the second group are responsible for inelastic lifetime making it anomalously short, so that the concept of quasiparticles applies to these electrons only marginally. We also demonstrate that interactions renormalize the spectrum of electrons in the vicinity of topological transition, the parameters of renormalized spectrum being strongly dependent on the proximity to the transition. Another many-body effect that evolves dramatically as the Fermi level is swept through the transition is the Friedel oscillations of the electron density created by electrons of the second group around an impurity. These oscillations are strongly anisotropic with a period depending on the direction. Scattering of electrons off these oscillations give rise to a temperature-dependent ballistic correction to the conductivity.

cond-mat.dis-nn↗

arXiv2019

Binding Energy and Lifetime of Excitons in Metallic Nanotubes

The difficulty of describing excitons in semiconducting SWNTs analytically lies with the fact that excitons can neither be considered strictly 1D nor 2D objects. However, the situation changes in the case of metallic nanotubes where, by virtue of screening from gapless metallic subbands, the radius of the exciton becomes much larger than the radius of the nanotube $R_\text{ex}\gg R$. Taking advantage of this, we develop the theory of excitons in metallic nanotubes, determining that their binding energy is about $0.08v/R$, in agreement with the existing experimental data. Additionally, because of the presence of the gapless subbands, there are processes where bound excitons are scattered into unbound electron-hole pairs belonging to the gapless subbands. Such processes lead to a finite exciton lifetime and the broadening of its spectral function. We calculate the corresponding decay rate of the excitons.

cond-mat.mes-hall↗

arXiv2018

Potential and spin-exchange interaction between Anderson impurities in graphene

The effective interaction between resonant magnetic Anderson impurities in graphene, mediated by conduction electrons, is studied as a function of the strength of the onsite energy level of the impurities and the amplitude of coupling to conduction electrons. The sign and character of the interaction depend on whether the impurities reside on the same or opposite sublattices. For the same (opposite) sublattice, the potential interaction is attractive (repulsive) in the weak coupling limit with $1/R^3$ dependence on the distance; the interaction reverses sign and becomes repulsive (attractive) in the strong coupling limit and displays $1/R$ behavior. The spin-exchange coupling is ferromagnetic (antiferromagnetic) at both large and small distances, but reverses sign and becomes anti-ferromagnetic (ferromagnetic) for intermediate distances. For opposite sublattices, the effective spin exchange coupling is resonantly enhanced at distances where the energy levels cross the Dirac points.

cond-mat.mes-hall↗

arXiv2017

Breakdown of classical electrostatics in the depolarization of quantum wires and nanotubes

In quantum wires, such as metallic nanotubes, the optical absorption of the transverse polarization is controlled by the depolarization effect which stems from the redistribution of conduction electrons around the circumference of the system. The traditional electrostatics treatment of the depolarization effect relies on approximating the system by a cylinder with some effective dielectric permittivity. We demonstrate that this simple intuitive picture does not adequately describe optical absorption near its threshold, as the depolarization effect becomes dominated by many-body correlations which strongly modify the spectral dependence of absorption.

cond-mat.mes-hall↗

arXiv2017

Suppression of the Landau-Zener transition probability by a weak classical noise

When the drive which causes the level crossing in a qubit is slow, the probability, P_{LZ}, of the Landau-Zener transition is close to 1. We show that in this regime, which is most promising for applications, the noise due to the coupling to the environment, reduces the average P_{LZ}. At the same time, the survival probability, 1-P_{LZ}, which is exponentially small for a slow drive, can be completely dominated by noise-induced correction. Our main message is that the effect of a weak classical noise can be captured analytically by treating it as a perturbation in the Schroedinger equation. This allows us to study the dependence of the noise-induced correction to P_{LZ} on the correlation time of the noise. As this correlation time exceeds the bare Landau-Zener transition time, the effect of noise becomes negligible. We consider two conventional realizations of noise: Gaussian noise and telegraph noise.

cond-mat.mes-hall↗

arXiv2017

Reversible temperature exchange upon thermal contact

According to a well-known principle of thermodynamics, the transfer of heat between two bodies is reversible when their temperatures are infinitesimally close. As we demonstrate, a little-known alternative exists: two bodies with temperatures different by an arbitrary amount can completely exchange their temperatures in a reversible way if split into infinitesimal parts that are brought into thermal contact sequentially.

physics.pop-ph↗

arXiv2016

Long-range exchange interaction between magnetic impurities in graphene

The effective spin exchange coupling between impurities (adatoms) on graphene mediated by conduction electrons is studied as a function of the strength of the potential part of the on-site energy $U$ of the electron-adatom interaction. With increasing $U$, the exchange coupling becomes long-range, determined largely by the impurity levels with energies close to the Dirac points. When adatoms reside on opposite sublattices, their exchange coupling, normally antiferromagnetic, becomes ferromagnetic and resonantly enhanced at a specific distance where an impurity level crosses the Dirac point.

cond-mat.mes-hall↗

arXiv2016

Density of states and magnetotransport in Weyl semimetals with long-range disorder

We study the density of states and magnetotransport properties of disordered Weyl semimetals, focusing on the case of a strong long-range disorder. To calculate the disorder-averaged density of states close to nodal points, we treat exactly the long-range random potential fluctuations produced by charged impurities, while the short-range component of disorder potential is included systematically and controllably with the help of a diagram technique. We find that for energies close to the degeneracy point, long-range potential fluctuations lead to a finite density of states. In the context of transport, we discuss that a self-consistent theory of screening in magnetic field may conceivably lead to non-monotonic low-field magnetoresistance.

cond-mat.mes-hall↗

arXiv2015

Attraction-repulsion transition in the interaction of adatoms and vacancies in graphene

The interaction of two resonant impurities in graphene has been predicted to have a long-range character with weaker repulsion when the two adatoms reside on the same sublattice and stronger attraction when they are on different sublattices. We reveal that this attraction results from a single energy level. This opens up a possibility of controlling the sign of the impurity interaction via the adjustment of the chemical potential. For many randomly distributed impurities (adatoms or vacancies) this may offer a way to achieve a controlled transition from aggregation to dispersion.

cond-mat.mes-hall↗

arXiv2015

Plasmon spectrum and plasmon-mediated energy transfer in a multi-connected geometry

Surface plasmon spectrum of a metallic hyperbola can be found analytically with the separation of variables in elliptic coordinates. The spectrum consists of two branches: symmetric, low-frequency branch, $ω<ω_0/\sqrt{2}$, and antisymmetric high-frequency branch, $ω>ω_0/\sqrt{2}$, where $ω_0$ is the bulk plasmon frequency. The frequency width of the plasmon band increases with decreasing the angle between the asymptotes of the hyperbola. For the simplest multi-connected geometry of two hyperbolas separated by an air spacer the plasmon spectrum contains two low-frequency branches and two high-frequency branches. Most remarkably, the lower of two low-frequency branches exists at $ω\rightarrow 0$, i.e., unlike a single hyperbola, it is "thresholdless." We study how the complex structure of the plasmon spectrum affects the energy transfer between two emitters located on the surface of the same hyperbola and on the surfaces of different hyperbolas.

cond-mat.mes-hall↗

arXiv2014

Manifestation of two-channel nonlocal spin transport in the shapes of the Hanle curves

Dynamics of charge-density fluctuations in a system of two tunnel-coupled wires contains two diffusion modes with dispersion iw=Dq^2 and iw =Dq^2+2/tau_t, where D is the diffusion coefficient and tau_t is the tunneling time between the wires. The dispersion of corresponding spin-density modes depends on magnetic field as a result of spin precession with Larmour frequency, w_L. The presence of two modes affects the shape of the Hanle curve describing the spin-dependent resistance, R, between ferromagnetic strips covering the non-magnetic wires. We demonstrate that the relative shapes of the R(w_L)-curves, one measured within the same wire and the other measured between the wires, depends on the ratio tau_t/tau_s, where tau_s is the spin-diffusion time. If the coupling between the wires is local, i.e. only at the point x=0, then the difference of the shapes of intra-wire and inter-wire Hanle curves reflects the difference in statistics of diffusive trajectories which "switch" or do not switch near x=0. When one of the coupled wires is bent into a loop with a radius, a, the shape of the Hanle curve reflects the statistics of random walks on the loop. This statistics is governed by the dimensionless parameter, a/(D tau_s)^(1/2).

cond-mat.mes-hall↗

arXiv2014

Equilibrium currents in chiral systems with non-zero Chern number

We describe simple quantum-mechanical approach to calculating equilibrium particle current along the edge of a system with non-trivial band spectrum topology. The approach does not require any a priori knowledge of the band topology and, as a matter of fact, treats topological and non-topological contributions to the edge currents on the same footing. We illustrate its usefulness by demonstrating the existence of `topologically non-trivial' particle currents along the edges of three different physical systems: two-dimensional electron gas with spin-orbit coupling and Zeeman magnetic field, surface state of a topological insulator, and kagome antiferromagnet with Dzyaloshinskii-Moriya interaction. We describe relation of our results to the notion of orbital magnetization.

cond-mat.mes-hall↗

arXiv2013

Dipole-induced localized plasmon modes and resonant surface plasmon scattering

A metal film supports the continuum of propagating surface plasmon waves. The interaction of these waves with a dipole (nanoparticle) positioned some distance from the surface of the film can produce well defined localized plasmon modes whose frequency nonetheless resides inside the continuum. This leads to the resonant enhancement of scattering of surface plasmons off the dipole. The maximum of scattering is found to occur when the distance from the dipole to the surface of the film is equal to one half of the film thickness. The possibility of controllable plasmon scattering could be advantageous for the field of nanoplasmonics.

cond-mat.mes-hall↗

arXiv2012

Resonant finite-size impurities in graphene, unitary limit and Friedel oscillations

Unitary limit for model point scatterers in graphene is known to reveal low-energy resonances. The same limit could be achieved from hybridization of band electrons with the localized impurity level positioned in the vicinity of the Fermi level. The finite size defects represent an easier realization of the effective unitary limit, occurring when the Fermi wavelength induced by the potential becomes of the order of the size of the defect. We calculate the induced electron density and find two signatures of a strong impurity, independent of its specific realization. The dependence of the impurity-induced electron density on the distance changes near resonances from ~r^{-3} to ~r^{-2}. The total number of induced particles at the resonance is equal to one per degree of spin and valley degeneracy. The effects of doping on the induced density are found.

cond-mat.mes-hall↗