arXiv subjects

A. Kashuba

Publications and source records attributed to A. Kashuba.

13 recordsLinked to original sources

arXiv2013

Critical phenomena in the bifurcation line's perspective

On the phase diagram of a system undergoing a continuous phase transition of the second order, three lines, hyper-surfaces, convergent into the critical point feature prominently: the ordered and disordered phases in the thermodynamic limit, and a third line, extending into a domain of finite-size systems, defined by the bifurcation of the distribution of the order parameter. Unlike critical phenomena in the thermodynamic limit devoid of known thermodynamic potential and described rather by the conformal symmetry, in finite-size systems near the bifurcation line an explicit Hamiltonian for the zero-mode of the order parameter is found. It bears the impress of the universality class of the critical point in terms of the two critical exponents: $β$ and $ν$.

cond-mat.stat-mech↗

arXiv2011

Susceptibility of the transverse field Ising model on the square lattice

Susceptibility of the transverse field Ising model on the square lattice is calculated numerically in the paramagnetic phase in a wide range of temperatures and transverse fields. An expression with one constant $π$, that determines both the critical exponent $γ$ and the critical transverse field, compellingly represents the data asymptotically near the quantum critical point, except for a narrow classical region close to the phase transition line, and shows two crossovers as temperature varies.

cond-mat.mes-hall↗

arXiv2008

Conductivity of the defectless Graphene

Conductivity of the defectless, perfect crystal graphene is found at the neutrality point at zero temperature and in the limit of large dielectric constant of the substrate. The steady state of the graphene with weak current is assumed to be an ideal, rare plasma of particle and hole excitations governed by the Boltzmann kinetic equation.

cond-mat.mtrl-sci↗

arXiv2006

Quantum crystal phase of electron liquid

A new bosonic, excitonic method for interacting electrons is developed. For two-dimensional electron liquid, it reveals a noncompensated quantum crystal phase ranging from the high density, or vanishing Coulomb interaction, limit: $r_s=0$, to a lower density $r_s\sim 10$, where a condensation of exciton pairs and the loss of the Fermi step is possible. The correlation energy and the static susceptibility, calculated using the method, are in agreement with the independent studies. A proof of the instability of the Fermi surface in the limit $r_s\to 0$ is given. The concept of quantum crystal is capable to explain the metal-insulator transition in Si field-effect heterostructures.

cond-mat.mtrl-sci↗

arXiv2005

Magneto-transport and divergent screening of driven two dimensional electron gas in high Landau levels

In two dimensional electron system in magnetic fields such that the Fermi energy lies in high Landau levels and driven by microwave $ac$-field a divergence of the Coulomb screening due to the Ryzhii photocurrent is predicted. A model of magneto-transport with superposition of long range and short range disorders is introduced. In this model the larger is the gradient of the long range potential the smaller is the longitudinal conductivity/resistivity. As a consequence a qualitative theory of the recently discovered zero-resistance states is given.

cond-mat.mes-hall↗

arXiv2005

Domain instability during precessional magnetization reversal

Spin wave equations in the non-equilibrium precessing state of a ferromagnetic system are found. They show a spin-wave instability towards growing domains of stable magnetization. Precession of the uniform magnetization mode is described by the Landau Lifshitz equation with the exponentially growing in time effective Gilbert dissipation constant that could have both signs. On the developed stages of the domain instability a non-stationary picture of domain chaos is observed.

cond-mat.mtrl-sci↗

arXiv2004

Two dimensional electron gas driven by strong alternating electric field

2D Fermi liquid driven by uniform alternating electric field at zero temperature may remain in quantum coherent non-equilibrium state. We develop a quasistatic approximation for strong and slow ac-fields and solve the problem of driven disordered 2D electron gas in high non-overlapping Landau levels. The broadening of Landau level has the Lorentz form and is inversely proportional to the amplitude of the ac-field. In the absence of electron-phonon interaction the electron distribution function is constant within the last Landau level and the diagonal dc-conductivity is zero. For weak electron-phonon interaction the dc-conductivity is anisotropic. A kinetic transition from the phonon cooling to the phonon heating is predicted.

cond-mat.mes-hall↗

arXiv2002

Possible Jahn-Teller effect in Si-inverse layers

Jahn-Teller effect in bivalley Si(100) MOSFET under conditions of quantum Hall effect at integer filling factors nu=1,2,3 is studied. This system is described by SU(4) hidden symmetry. At nu=2 static and dynamic lattice deformation creates an easy-plane anisotropy and antiferromagnetic exchange and lifts the valley degeneracy. At nu=1,3 Coulomb interaction is essential to produce weak easy-plane anisotropy. Three phases: ferromagnetic, canted antiferromagnetic and spin-singlet, have been found. Anisotropy energy of charged skyrmion excitation in every phase is found.

cond-mat.mes-hall↗

arXiv2002

Multicomponent dense electron gas as a model of Si MOSFET

We solve two-dimensional model of $N$-component dense electron gas in the limit of large $N$ and in a range of the Coulomb interaction parameter: $N^{-3/2}\ll r_s\ll 1$. The quasiparticle interaction on the Fermi circle vanishes as 1/N. The ground state energy and the effective mass are found as series in powers of $r_s^{2/3}$. In the quantum Hall state on the lowest Landau level at integer filling: $1\llν<N$, the charge activation energy gap and the exchange constant are found.

cond-mat.mes-hall↗

arXiv2001

Low temperature kinetics of 2D exciton gas cooling in quantum well bilayer

We study the kinetics of 2D Bose gas cooling provided Bose particles interact with 3D phonons. At low temperatures phonon emission is prohibited by the energy and the momentum conservation. We show that both particle-particle scattering and impurity scattering assist the Bose gas cooling.

cond-mat.mes-hall↗

arXiv2000

Conductivity activation energy for bilayer hetero-structures at integer filling numbers

We report on study of low-energy excitations in a bilayer hetero-structure 2D electron gas. We split the bilayer Hamiltonian into SU(4)-symmetric part and the anisotropy part and treat the latter as a perturbation. We find that both Goldstone and the charged excitations - skyrmions - are goverened by the non-linear Sigma Model. We calculate the anisotropic energy gap of the skyrmion to have a prominent minimum in the canted antiferromagnetic phase of bilayer. We compare our findings with the results of recent experiments.

cond-mat.mes-hall↗

arXiv1996

Long Wavelength Anomalous Diffusion Mode in the 2D XY Dipole Magnet

In 2D XY ferromagnet the dipole force induces a strong interaction between spin-waves in the long-wavelength limit. The major effect of this interaction is the transformation of a propagating spin-wave into a diffusion mode. We study the anomalous dynamics of such diffusion modes. We find that the Janssen-De Dominics functional, which governs this dynamics, approaches the non-Gaussian fixed-point. A spin-wave propagates by an anomalous anisotropic diffusion with the dispersion relation: $iω{\sim}k_{y}^{Δ_y}$ and $iω{\sim}k_{x}^{Δ_x}$, where ${Δ_y}=47/27$ and ${Δ_x}=47/36$. The low-frequency response to the external magnetic field is found.

cond-mat↗

arXiv1996

Spin Diffusion in 2D XY Ferromagnet with Dipolar Interaction

In the ordered phase of 2D XY ferromagnet the dipolar interaction between spins induces a strong, relevant interaction between spin-waves. We study quasi-excitations of the interacting spin-wave 'liquid' in the long wavelength limit. We employ the Janssen-De-Dominicis method for classical Langevin equation to find the transformation of the spin-wave excitation into a new soft-mode excitation in the intermediate range of wavelengths; and into an anomalous anisotropic diffusion mode excitation at long wavelengths. The dissipation of a spin-wave at short wavelengths is found to be highly anisotropic.

cond-mat↗