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Yury Sherkunov

Publications and source records attributed to Yury Sherkunov.

10 recordsLinked to original sources
arXiv2019

First order Fermi surface topological (Lifshitz) transition in an interacting two-dimensional Rashba Fermi liquid

We study the Fermi surface topological transition of the pocket-opening type in a two dimensional Fermi liquid with spin-orbit coupling of Rashba type. We find that the interactions, far from instabilities, drive the transition first order at zero temperature surprisingly in a more pronounced way than in the case of interacting Fermi liquid without spin-orbit coupling. We first gain insight from second order perturbation theory in the self-energy. We then extend the results to stronger interaction, using the self-consistent fluctuation approximation. We discuss existing experimental work on the system BiTeI and suggest further experiments in the light of these results .

cond-mat.str-el↗
arXiv2018

Novel phases in twisted bilayer graphene at magic angles as a result of van Hove singularities and interactions

The discovery of different phases as a result of correlations, especially in low-dimensional materials, has been always an exciting and fundamental subject of research. Recent experiments on twisted bilayer graphene have revealed reentrant unconventional superconductivity as a function of doping as well as a Mott-like insulating phase when the two layers are twisted with respect to each other at certain "magic" angles for doping corresponding to two particles per moire unit cell. In this work we propose a microscopic model that takes into account interactions and the van Hove singularities in the density of states of the twisted bilayer graphene at doping corresponding to one particle ($ν$ =1) per moiré unit cell and study how superconductivity emerges. We identify the possible symmetry of the order parameter as $s^{\pm}$, while if the inter-valley coupling is negligible the symmetry is $s^{++}$. In addition, we find and characterise the insulating region of the system, as a region with a uniform charge instability where there is coexistence of the metallic and insulating phases.

cond-mat.str-el↗
arXiv2018

Effects of Lifshitz transitions in ferromagnetic superconductors: the case of URhGe

In ferromagnetic superconductors, like URhGe, superconductivity co-exists with magnetism near zero field, but then re-appears again in a finite field range, where the system also displays mass enhancement in the normal state. We present theoretical understanding of this non-monotonic behavior. We explore the multi-band nature of URhGe and associate re-entrant superconductivity and mass enhancement with the finite field Lifshitz transition in one of the bands. We found good agreement between our theory and a number of experimental results for URhGe, such as weakly first order reentrant transition, the dependence of superconducting $T_c$ on a magnetic field, and the field dependence of the effective mass, the specific heat and the resistivity in the normal state. Our theory can be applied to other ferromagnetic multi-band superconductors.

cond-mat.str-el↗
arXiv2018

Resonance oscillations of non-reciprocal long-range van der Waals forces between atoms in electromagnetic fields

We study theoretically the van der Waals interaction between two atoms out of equilibrium with isotropic electromagnetic field. We demonstrate that at large interatomic separations, the van der Waals forces are resonant, spatially oscillating and non-reciprocal due to resonance absorption and emission of virtual photons. We suggest that the van der Waals forces can be controlled and manipulated by tuning the spectrum of artificially created random light.

quant-ph↗
arXiv2010

Casimir-Polder Potential in Thermal Non-Equilibrium

Different non-equilibrium situations have recently been considered when studying the thermal Casimir--Polder interaction with a body. We show that the Keldysh Green function method provides a very general common framework for such studies where non-equilibrium of either the atom or the body with the environment can be accounted for. We apply the results to the case of ground state polar molecules out of equilibrium with their environment, observing several striking effects. We consider thermal Casimir--Polder potentials in planar configurations, and new results for a molecule in a cylindrical cavity are reported, showing similar characteristic behaviour as found in planar geometry.

quant-ph↗
arXiv2008

Dispersion interaction between two atoms in electromagnetic fields

We present a new theory of atom-atom dispersion interaction in the presence of electromagnetic fields. The theory takes into account the absorption and emission of virtual photons leading to the resonance contributions to the interaction potential in the case of non-equilibrium dynamics.

quant-ph↗
arXiv2006

Casimir interaction between gas media of excited atoms

The retarded dispersion interaction (Casimir interaction) between two dilute dielectric media at high temperatures is considered. The excited atoms are taken into account. It is shown that the perturbation technique can not be applied to this problem due to the divergence of integrals. A non-perturbative approach based on kinetic Green functions is implemented. We consider interaction between two atoms (one of them is excited0 embedded in an absorbing dielectric medium. We take into account possible absorption of photons in the medium, which solves the problem of divergence. The force between two plane dilute dielectric media is calculated at pair interaction approximation. We show that the result of quantum electrodynamics differs from the Lifshitz formula for dilute gas media at high temperatures (if the number of excited atoms is significant). According to quantum electrodynamics, the interaction may be either attractive or repulsive depending on the temperature and the density numbers of the media.

quant-ph↗
arXiv2006

Casimir-Polder interaction between an excited atom and a gas dielectric medium

The Casimir-Polder potential for interaction between an excited atom and a ground-state one in the retarded case obtained with the help of perturbation technique drops as R^-2 with the distance between the atoms [E.A. Power, T.Thirunamachandran, Phys. Rev. A, 47, 2539 (1993)]. It results in diverdent integrals for interaction between an excited atom and a dilute gas medium. We investigate interaction between two atoms embedded in a dielectric medium with the help of non-perturbative approach. We take into account absorption of photons in the medium. This approach solves the problem of divergence. We consider interaction between an excited atom and a planar dielectric gas medium of ground-state atoms. We show that the retarded interaction between an excited atom and a gas of ground-state atoms is not oscillating but follows a simple power law. We show that to obtain coventional non-retarded expression for the van der Waals force between an excited atom and a dilute gas the distance between the atom and the interface should be much smaller than the free mean pass of a photon in the medium. Interaction between an excited atom and a hemisphere of ground-state atoms is considered.

quant-ph↗
arXiv2006

Casimir interaction between excited media in electromagnetic field

We investigate the Casimir-Polder interaction between two atoms one of which is excited. We show that the perturbation theory results in divergence of integrals for the interaction between an excited atom and a media of dilute gas. We considered the interaction between two atoms embedded in a dielectric medium. The non-perturbative method used in this paper shows that the interaction between the atoms is suppressed due to absorption of photons by the medium. Now the integrals are divergent no more. Interaction between two media of dilute gases is considered for the case of high temperatures.

quant-ph↗