arXiv subjects

Yasha Gindikin

Publications and source records attributed to Yasha Gindikin.

At least 19 recordsLinked to original sources

arXiv2025

Collective excitations and stability of a non-Fermi liquid state near a quantum-critical point of a metal

We examine the spectral properties of collective excitations with finite angular momentum $l$ for a system of interacting fermions near a Pomeranchuk quantum critical point, both in the Fermi liquid and non-Fermi liquid regimes. Previous studies found that deep in the Fermi liquid regime, the spectral functions for even and odd $l$ behave differently - the latter is suppressed compared to the former because of kinematic constraints on scattering processes. The main focus of our paper is to understand how the spectral functions for even and odd $l$ evolve as the system enters the non-Fermi liquid regime. We obtain the full scaling function for the electron polarization bubble at arbitrary $l$, which interpolates between the Fermi liquid and non-Fermi liquid regimes. We show that collective excitations for all $l$ remain stable and causal throughout the crossover and right at the quantum critical point.

cond-mat.str-el↗

arXiv2025

Electron Interactions in Rashba Materials

We present a bunch of novel phenomena stemming from the pair spin-orbit interaction (PSOI), which does not rely on structure inversion asymmetry but instead arises from Coulomb fields of interacting electrons in materials with a strong Rashba effect. First, PSOI can induce $p-$wave superconducting order without the need for any mediators of attraction. Depending on the sign and strength of the PSOI coupling, two distinct superconducting phases emerge in 3D systems, analogous to the A and B phases observed in superfluid $^3\mathrm{He}$. In contrast, 2D systems exhibit $p^x\pm i p^y$ order parameter, leading to the time-reversal-invariant topological superconductivity. Second, a sufficiently strong PSOI can induce ferromagnetic ordering. It is associated with a deformation of the Fermi surface, which eventually leads to a Lifshitz transition from a spherical to a toroidal Fermi surface, with a number of experimentally observable signatures. Finally, in sufficiently clean Rashba materials, ferromagnetism and $p-$wave superconductivity may coexist. This state resembles the $\mathrm{A}_1$ phase of $^3\mathrm{He}$, yet it may avoid nodal points due to the toroidal shape of the Fermi surface.

cond-mat.supr-con↗

arXiv2024

Quantum criticality and optical conductivity in a two-valley system

We demonstrate that the optical conductivity of a Fermi liquid (FL) in the absence of umklapp scattering is dramatically affected by the topology of the Fermi surface (FS). Specifically, electron-electron (ee) scattering leads to rapid current relaxation in systems with multiple, or multiply connected, FSs, provided the valleys have different effective masses. This effect results from intervalley drag. We microscopically derive the optical conductivity of a two-valley system, both within the FL regime and near a quantum critical point (QCP) of the Ising-nematic type. In the FL regime, intervalley drag restores the Gurzhi-like scaling of the conductivity, $\mathrm{Re} σ(ω) \sim ω^0$. This dependence contrasts sharply with the previously identified sub-leading contribution to the conductivity of a two-dimensional FL with a single convex FS, where $\mathrm{Re} σ(ω) \sim ω^2 \ln |ω|$. The vanishing of the leading term in the optical conductivity is a signature of geometric constraints on ee scattering channels, which are lifted for a multiply connected FS. A large differential response, $d \mathrm{Re} σ/d μ$ with $μ$ being the chemical potential, is predicted at the Lifshitz transition from a single-valley to a multi-valley FS, which should be observable within the experimentally accessible frequency range. Near a QCP, intervalley drag leads to a $|ω|^{-2/3}$ scaling of $\mathrm{Re} σ(ω)$ in 2D, thus providing a specific current-relaxing process for this long-standing conjecture.

cond-mat.str-el↗

arXiv2024

Fermi Surface Geometry and Optical Conductivity of a 2D Electron Gas near an Ising-Nematic Quantum Critical Point

We analyze optical conductivity of a clean two-dimensional electron system in a Fermi liquid regime near a $T=0$ Ising-nematic quantum critical point (QCP), and extrapolate the results to a QCP. We employ direct perturbation theory up to the two-loop order to elucidate how the Fermi surface's geometry (convex vs. concave) and fermionic dispersion (parabolic vs. non-parabolic) affect the scaling of the optical conductivity, $σ(ω)$, with frequency $ω$ and correlation length $ξ$. We find that for a convex Fermi surface the leading terms in the optical conductivity cancel out, leaving a sub-leading contribution $σ(ω) \propto ω^2 ξ^4 \mathcal{L}$, where $\mathcal{L} = \mathrm{const}$ for a parabolic dispersion and $\mathcal{L} \propto \log{ωξ^3}$ in a generic case. For a concave Fermi surface, the leading terms do not cancel, and $σ(ω) \propto ξ^2$. We extrapolate these results to a QCP and obtain $σ(ω) \propto ω^{2/3}$ for a convex Fermi surface and $σ(ω) \propto 1/ω^{2/3}$ for a concave Fermi surface.

cond-mat.str-el↗

arXiv2023

Electron correlations due to pair spin-orbit interaction in 2D electron systems

We show that the pair spin-orbit interaction (PSOI) created by the Coulomb fields of interacting electrons leads to the appearance of an unconventional correlated electronic state in two-dimensional materials with the large Rashba effect. The effect manifests itself at sufficiently strong PSOI as a sharp peak in the structure factor, indicating a tendency to form a striped structure with a spatial scale determined by the competition between the Coulomb repulsion and the PSOI-induced attraction of electrons. Above the critical value of PSOI, the system becomes unstable with respect to the charge density fluctuations on this scale.

cond-mat.str-el↗

arXiv2023

Spin-dependent electron-electron interaction in Rashba materials

We review the effects of the pair spin-orbit interaction (PSOI) in Rashba materials. The PSOI is the electron-electron interaction component that depends on the spin and momentum of the electrons. Being produced by the Coulomb fields of interacting electrons, it exists already in vacuum, but becomes orders of magnitude larger in materials with the giant Rashba effect. The main nontrivial feature of the PSOI is that it is attractive for electrons in certain spin configurations tied to their momentum and competes with the Coulomb repulsion of the electrons. Under certain conditions attainable in modern low-dimensional structures the PSOI prevails. The resulting attraction between electrons leads to the formation of bound electron pairs, the binding energy of which can be controlled by electrical means. In many-electron systems the PSOI results in the instabilities of the uniform ground state with respect to the density fluctuations, which develop on different spatial scales, depending on the geometry of the electric fields that produce the PSOI. If the PSOI is not too strong the electronic system is stable, but its collective excitations reveal the highly unusual spin-charge structure and spectrum, which manifest themselves in the frequency dependence of the dynamic conductivity.

cond-mat.str-el↗

arXiv2022

Electron pairs bound by the spin-orbit interaction in 2D gated Rashba materials with two-band spectrum

We show that the bound electron pairs (BEPs) emerge in two-dimensional gated Rashba materials owing to the interplay of the pair spin-orbit interaction, produced by the Coulomb fields of interacting electrons, and the peculiarities of the band structure giving rise to a negative reduced mass of the interacting electrons. Our consideration is based on the four-band Bernevig-Hughes-Zhang model with the Rashba spin-orbit interaction created by the charges on the gate. The binding energy of the BEP varies with the gate voltage in a wide range across the entire width of the two-particle energy gap. Although the spin-orbit interaction destroys the spin quantization, the BEPs have a magnetic moment, which is created mainly by the orbital motion of the electrons and tuned by the gate voltage.

cond-mat.mes-hall↗

arXiv2020

The Coulomb impurity in 2D materials with strong spin-orbit interaction

We show that the spin-orbit interaction (SOI) produced by the Coulomb fields of charged impurities provides an efficient mechanism for the bound states formation. The mechanism can be realized in 2D materials with sufficiently strong Rashba SOI provided that the impurity locally breaks the structure inversion symmetry in the direction normal to the layer.

cond-mat.mes-hall↗

arXiv2020

The spin-orbit mechanism of electron pairing in quantum wires

We solve a two-body problem for electrons in a one-dimensional system to show that two-electron bound states can arise as a result of the image-potential-induced spin-orbit interaction (iSOI). The iSOI contributes an attractive component to the electron-electron interaction Hamiltonian that competes with the Coulomb repulsion and overcomes it under certain conditions. We find that there exist two distinct types of two-electron bound states, depending on the type of the motion that forms the iSOI: the relative motion or the motion of the electron pair as a whole. The binding energy lies in the meV range for realistic material parameters and is tunable by the gate potential.

cond-mat.str-el↗

arXiv2020

Bound electron pairs formed by the spin-orbit interaction in 2D gated structures

We explore the bound electron pairs (BEPs) arising due to the pair spin-orbit interaction (PSOI) in two-dimensional structures with a gate that can allow the BEPs to be manipulated. The gate breaks the in-plane reflection symmetry of the pair Coulomb field and creates a one-particle Rashba spin-orbit interaction. We find that the normal component of the electric field substantially affects the BEPs but the key role in forming the BEPs belongs to the in-plane component. The ground state of a BEP with zero total momentum, which is doubly degenerate in the absence of the gate, splits into two states. One of them is tunable by varying the gate voltage whereas the other is on the contrary robust. The tunable BEP has a higher binding energy which grows as the gate voltage increases, with its orbital and spin structure changing continuously. At the large negative voltage the tunable BEP decays. The orbital and spin structure of the robust BEP does not depend on the gate voltage. Its energy level crosses the conduction band bottom at high gate voltage of any polarity, but the robust BEP remains bound and localized even when in continuum.

cond-mat.str-el↗

arXiv2020

Spin-orbit-driven electron pairing in two dimensions

We show that the spin-orbit interaction (SOI) arising due to the in-plane electric field of the Coulomb repulsion between electrons in a two-dimensional quantum well produces an attractive component in the pair interaction Hamiltonian that depends on the spins and momenta of electrons. If the Rashba SOI constant of the material is high enough the attractive component overcomes the Coulomb repulsion and the centrifugal barrier, which leads to the formation of the two-electron bound states. There are two distinct types of two-electron bound states. The relative bound states are formed by the electrons orbiting around their common barycenter. They have the triplet spin structure and are independent of the center-of-mass momentum. In contrast, the convective bound states are formed because of the center-of-mass motion, which couples the electrons with opposite spins. The binding energy in the meV range is attainable for realistic conditions.

cond-mat.str-el↗

arXiv2020

Pair spin-orbit interaction in low-dimensional electron systems

The pair spin-orbit interaction (PSOI) is the spin-orbit component of the electron-electron interaction that originates from the Coulomb fields of the electrons. This relativistic component, which has been commonly assumed small in the low-energy approximation, appears large and very significant in materials with the strong SOI. The PSOI, being determined by the spins and momenta of electrons, has highly unusual properties among which of most interest is the mutual attraction of the electrons in certain spin configurations. We review the nature of the PSOI in solids and its manifestations in low-dimensional systems that have been studied to date. The specific results depend on the configuration of the Coulomb fields in a particular structure. The main actual structures are considered: one-dimensional quantum wires and two-dimensional layers, both suspended and placed in various dielectric media, as well as in the presence of a metallic gate. We discuss the possible types of the two-electron bound states, the conditions of their formation, their spectra together with the spin and orbital structure. In a many-particle system, the PSOI breaks the spin-charge separation as a result of which spin and charge degrees of freedom are mixed in the collective excitations. At sufficiently strong PSOI, one of the collective modes softens. This signals of the instability, which eventually leads to the reconstruction of the homogeneous state of the system.

cond-mat.str-el↗

arXiv2019

Deformed Wigner crystal in a one-dimensional quantum dot

The spatial Fourier spectrum of the electron density distribution in a finite 1D system and the distribution function of electrons over single-particle states are studied in detail to show that there are two universal features in their behavior, which characterize the electron ordering and the deformation of Wigner crystal by boundaries. The distribution function has a $δ$-like singularity at the Fermi momentum $k_F$. The Fourier spectrum of the density has a step-like form at the wavevector $2k_F$, with the harmonics being absent or vanishing above this threshold. These features are found by calculations using exact diagonalization method. They are shown to be caused by Wigner ordering of electrons, affected by the boundaries. However the common Luttinger liquid model with open boundaries fails to capture these features, because it overestimates the deformation of the Wigner crystal. An improvement of the Luttinger liquid model is proposed which allows one to describe the above features correctly. It is based on the corrected form of the density operator conserving the particle number.

cond-mat.str-el↗

arXiv2018

Coulomb pairing of electrons in thin films with strong spin-orbit interaction

In low-dimensional structures with strong Rashba spin-orbit interaction (SOI), the Coulomb fields between moving electrons produce a SOI component of the pair interaction that competes with the potential Coulomb repulsion. If the Rashba SOI constant of the material is sufficiently high, the total electron-electron interaction becomes attractive, which leads to the formation of the two-electron bound states. We show that because of the dielectric screening in a thin film the binding energy is significantly higher as compared to the case of the bulk screening.

cond-mat.str-el↗

arXiv2017

Dynamic transport in a quantum wire driven by spin-orbit interaction

We consider a gated one-dimensional (1D) quantum wire disturbed in a contactless manner by an alternating electric field produced by a tip of a scanning probe microscope. In this schematic 1D electrons are driven not by a pulling electric field but rather by a non-stationary spin-orbit interaction (SOI) created by the tip. We show that a charge current appears in the wire in the presence of the Rashba SOI produced by the gate net charge and image charges of 1D electrons induced on the gate (iSOI). The iSOI contributes to the charge susceptibility by breaking the spin-charge separation between the charge- and spin collective excitations, generated by the probe. The velocity of the excitations is strongly renormalized by SOI, which opens a way to fine-tune the charge and spin response of 1D electrons by changing the gate potential. One of the modes softens upon increasing the gate potential to enhance the current response as well as the power dissipated in the system.

cond-mat.str-el↗

arXiv2017

Dynamics of one-dimensional electrons with broken spin-charge separation

Spin-charge separation is known to be broken in many physically interesting one-dimensional (1D) and quasi-1D systems with spin-orbit interaction because of which spin and charge degrees of freedom are mixed in collective excitations. Mixed spin-charge modes carry an electric charge and therefore can be investigated by electrical means. We explore this possibility by studying the dynamic conductance of a 1D electron system with image-potential-induced spin-orbit interaction. The real part of the admittance reveals an oscillatory behavior versus frequency that reflects the collective excitation resonances for both modes at their respective transit frequencies. By analyzing the frequency dependence of the conductance the mode velocities can be found and their spin-charge structure can be determined quantitatively.

cond-mat.str-el↗

arXiv2017

Image-potential-induced spin-orbit interaction in one-dimensional electron systems

We study the spin-orbit interaction effects in a one-dimensional electron system that result from the image charges in a nearby metallic gate. The nontrivial property of the image-potential-induced spin-orbit interaction (iSOI) is that it directly depends on the electron density because of which a positive feedback arises between the electron density and the iSOI magnitude. As a result, the system becomes unstable against the density fluctuations under certain conditions. In addition, the iSOI contributes to the electron-electron interaction giving rise to strong changes in electron correlations and collective excitation spectra. We trace the evolution of the spectrum of the collective excitations and their spin-charge structures with the change in the iSOI parameter. One out of two collective modes softens as the iSOI amplitude grows to become unstable at its critical value. Interestingly, this mode evolves from a pure spin excitation to a pure charge one. At the critical point its velocity turns to zero together with the charge stiffness.

cond-mat.str-el↗

arXiv2017

Effect of short-range electron correlations in dynamic transport in a Luttinger liquid

The density operator in the Luttinger model consists of two components, one of which describes long-wave fluctuations and the other is related to the rapid oscillations of the charge-density-wave (CDW) type, caused by short-range electron correlations. It is commonly believed that the conductance is determined by the long-wave component. The CDW component is considered only when an impurity is present. We investigate the contribution of this component to the dynamic density response of a Luttinger liquid free from impurities. We show that the conventional form of the CDW density operator does not conserve the number of particles in the system. We propose the corrected CDW density operator devoid of this shortcoming and calculate the dissipative conductance in the case when the one-dimensional conductor is locally disturbed by a conducting probe. The contribution of the CDW component to conductance is found to dominate over that of the long-wave component in the low-frequency regime.

cond-mat.str-el↗