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A. A. Donkov

Publications and source records attributed to A. A. Donkov.

7 recordsLinked to original sources
arXiv2016

Energy spectra of a spin-$\tfrac12$ XY spin molecule interacting with a single mode field cavity: Numerical study

In a previous paper [J. Phys.: Conf. Ser. 682 (2016) 012032}, arXiv:1605.05593] we studied analytically the energy spectra of a finite-size spin $\tfrac12$ XY chain (molecule) coupled at an arbitrary spin site to a single mode of an electromagnetic field via the Jaynes-Cummings model. We considered spin rings and open spin molecules with up to 4 spins and an interaction restricted to nearest-neighbours. Here we extend our investigation, addressing numerically the energy spectra of molecules of up to 10 spins with nearest-neighbour or long-range interaction. Furthermore we analyze the behaviour of an invariant operator, constructed by combining the magnetization of the spin-chain and the total number of photons in the system. We found a strong dependence on the number (even or odd) of sites in the molecules. This study is aimed at finding the appropriate combination of the physical parameters that could make the system suitable for use in quantum computations.

quant-ph↗
arXiv2016

Interaction of a single mode field cavity with the 1D XY model: Energy spectrum

In this work we use the fundamental in quantum optics Jaynes-Cummings model to study the response of spin $\tfrac12$ chain to a single mode of a laser light falling on one of the spins, a focused interaction model between the light and the spin chain. For the spin-spin interaction along the chain we use the XY model. We report here the exact analytical results, obtained with the help of a computer algebra system, for the energy spectrum in this model for chains of up to 4 spins with nearest neighbors interactions, either for open or cyclic chain configurations. Varying the sign and magnitude of the spin exchange coupling relative to the light-spin interaction we have investigated both cases of ferromagnetic or antiferromagnetic spin chains.

quant-ph↗
arXiv2011

Momentum and Mass Fluxes in a Gas Confined between Periodically Structured Surfaces at Different Temperatures

It is well known that in a gas-filled duct or channel along which a temperature gradient is applied, a thermal creep flow is created. Here we show that a mass and momentum flux can also be induced in a gas confined between two parallel structured surfaces at different temperatures, i.e. \textit{orthogonal} to the temperature gradient. We use both analytical and numerical methods to compute the resulting fluxes. The momentum flux assumes its maximum value in the free-molecular flow regime, the (normalized) mass flux in the transition flow regime. The discovered phenomena could find applications in novel methods for energy-conversion and thermal pumping of gases.

physics.flu-dyn↗
arXiv2000

Superconducting gap anisotropy within the framework of a simple exchange model for layered cuprates. The theory of HTSC

The oxygen O2p_sigma and copper Cu4s and Cu3d_x^2-y^2 orbitals are involved in a simple LCAO model for determination of the conduction band and the oxygen-oxygen hopping is considered as a small parameter with respect to the transition amplitude between nearest neighbours. The traditional Cooper pairing is obtained by taking into account the double-electron exchange between the nearest neighbours within the two-dimensional CuO_2 plane. The equation for the superconducting gap is obtained as a result of the standard BCS treatment. It is shown that the order parameter could have either s-type or d-type symmetry depending on the ratio between the transition amplitudes. This model allows understanding the experiments reporting a pi-shift of the Josephson phase indicative for a d-type gap symmetry as well as the observed s-type in the case of strongly irradiated samples.

cond-mat.supr-con↗