arXiv subjects

Igor S. Burmistrov

Publications and source records attributed to Igor S. Burmistrov.

10 recordsLinked to original sources

arXiv2023

Generalized surface multifractality in 2D disordered systems

Recently, a concept of generalized multifractality, which characterizes fluctuations and correlations of critical eigenstates, was introduced and explored for all ten symmetry classes of disordered systems. Here, by using the non-linear sigma-model field theory, we extend the theory of generalized multifractality to boundaries of systems at criticality. Our numerical simulations on two-dimensional (2D) systems of symmetry classes A, C, and AII fully confirm the analytical predictions of pure-scaling observables and Weyl symmetry relations between critical exponents of surface generalized multifractality. This demonstrates validity of the non-linear sigma-model field theory for description of Anderson-localization critical phenomena not only in the bulk but also on the boundary. The critical exponents strongly violate generalized parabolicity, in analogy with earlier results for the bulk, corroborating the conclusion that the considered Anderson-localization critical points are not described by conformal field theories. We further derive relations between generalized surface multifractal spectra and linear combinations of Lyapunov exponents of a strip in quasi-one-dimensional geometry, which hold under assumption of invariance with respect to a logarithmic conformal map. Our numerics demonstrate that these relations hold with an excellent accuracy. Taken together, our results indicate an intriguing situation: the conformal invariance is broken but holds partially at critical points of Anderson localization.

cond-mat.dis-nn↗

arXiv2019

Unrestricted electron bunching at the helical edge

A quantum magnetic impurity of spin $S$ at the edge of a two-dimensional time reversal invariant topological insulator may give rise to backscattering. We study here the shot noise associated with the backscattering current for arbitrary $S$. Our full analytical solution reveals that for $S>\frac{1}{2}$ the Fano factor may be arbitrarily large, reflecting bunching of large batches of electrons. By contrast, we rigorously prove that for $S=\frac{1}{2}$ the Fano factor is bounded between $1$ and $2$, generalizing earlier studies.

cond-mat.mes-hall↗

arXiv2019

Current noise geometrically generated by a driven magnet

We consider a non-equilibrium cross-response phenomenon, whereby a driven magnetization gives rise to electric shot noise (but no d.c. current). This effect is realized on a nano-scale, with a small metallic ferromagnet which is tunnel-coupled to two normal metal leads. The driving gives rise to a precessing magnetization. The geometrically generated noise is related to a non-equilibrium distribution in the ferromagnet. Our protocol provides a new channel for detecting and characterizing ferromagnetic resonance.

cond-mat.mes-hall↗

arXiv2018

A thermally driven spin-transfer-torque system far from equilibrium: enhancement of the thermoelectric current via pumping current

We consider a small itinerant ferromagnet exposed to an external magnetic field and strongly driven by a thermally induced spin current. For this model, we derive the quasi-classical equations of motion for the magnetization where the effects of a dynamical non-equilibrium distribution function are taken into account self-consistently. We obtain the Landau-Lifshitz-Gilbert equation supplemented by a spin-transfer torque term of Slonczewski form. We identify a regime of persistent precessions in which we find an enhancement of the thermoelectric current by the pumping current.

cond-mat.mes-hall↗

arXiv2016

Strong non-equilibrium effects in spin torque systems

We consider a problem of persistent magnetization precession in a single domain ferromagnetic nano particle under the driving by the spin-transfer torque. We find that the adjustment of the electronic distribution function in the particle renders this state unstable. Instead, abrupt switching of the spin orientation is predicted upon increase of the spin-transfer torque current. On the technical level, we derive an effective action of the type of Ambegaokar-Eckern-Schön action for the coupled dynamics of magnetization (gauge group $SU(2)$) and voltage (gauge group $U(1)$).

cond-mat.mes-hall↗

arXiv2015

U(1) and SU(2) quantum dissipative systems: The Caldeira-Leggett vs. the Amegaokar-Eckern-Schön approaches

There are two paradigmatic frameworks for treating quantum systems coupled to a dissipative environment: the Caldeira-Leggett and the Ambegaokar-Eckern-Schön approaches. Here we recall the differences between them, and explain the consequences when each is applied to a zero dimensional spin (possessing an SU(2) symmetry) in a dissipative environment (a dissipative quantum dot near or beyond the Stoner instability point).

cond-mat.mes-hall↗

arXiv2015

Geometric Quantum Noise of Spin

The presence of geometric phases is known to affect the dynamics of the systems involved. Here we consider a quantum degree of freedom, moving in a dissipative environment, whose dynamics is described by a Langevin equation with quantum noise. We show that geometric phases enter the stochastic noise terms. Specifically, we consider small ferromagnetic particles (nano-magnets) or quantum dots close to Stoner instability, and investigate the dynamics of the total magnetization in the presence of tunneling coupling to the metallic leads. We generalize the Ambegaokar-Eckern-Schön (AES) effective action and the corresponding semiclassical equations of motion from the U(1) case of the charge degree of freedom to the SU(2) case of the magnetization. The Langevin forces (torques) in these equations are strongly influenced by the geometric phase. As a first but nontrivial application we predict low temperature quantum diffusion of the magnetization on the Bloch sphere, which is governed by the geometric phase. We propose a protocol for experimental observation of this phenomenon.

cond-mat.mes-hall↗

arXiv2006

Conductance oscillations with magnetic field of a two-dimensional electron gas-superconductor junction

We find the current voltage characteristics of a 2DEG-S interface in magnetic field taking into account the surface roughness. Typically in experiments $L/2R_c\gtrsim 3$, where $L$ is the surface length and $R_c$ is the cyclotron radius. The conductance behaves in experiments usually as $G=g_0+g_1\cos(2πν+δ_1)$; higher harmonics, $g_2\cos(4πν+δ_2),...$, are hardly seen. Theories based on the assumption of the interface perfectness can hardly describe qualitatively the visibility of the condctance oscillations and the amplitudes of the harmonics: they predict $g_1\sim g_2\sim g_3,...$. Our approach with the surface roughness qualitatively agrees with experiments. It is shown how a disorder at a 2DEG-S interface suppresses the conductance oscillations with $ν$.

cond-mat.mes-hall↗

arXiv2003

Andreev conductance of a domain wall

At low temperatures, the transport through a superconductor-ferromagnet tunnel interface is due to tunneling of electrons in pairs. Exchange field of a monodomain ferromagnet aligns electron spins and suppresses the two electron tunneling. The presence of the domain walls at the SF interface strongly enhances the subgap current. The Andreev conductance is proven to be proportional to the total length of domain walls at the SF interface.

cond-mat.supr-con↗

arXiv2003

Mean-field Phase Diagram of Two-Dimensional Electrons with Disorder in a Weak Magnetic Field

We study two-dimensional interacting electrons in a weak perpendicular magnetic field with the filling factor $ν\gg 1$ and in the presence of a quenched disorder. In the framework of the Hartree-Fock approximation, we obtain the mean-field phase diagram for the partially filled highest Landau level. We find that the CDW state can exist if the Landau level broadening $1/2τ$ does not exceed the critical value $1/2τ_{c}=0.038ω_{H}$. Our analysis of weak crystallization corrections to the mean-field results shows that these corrections are of the order of $(1/ν)^{2/3}\ll 1$ and therefore can be neglected.

cond-mat.mes-hall↗