arXiv subjects

Sergei N. Klimin

Publications and source records attributed to Sergei N. Klimin.

4 recordsLinked to original sources

arXiv2019

Plasmonic Cooper pairing in single layer graphene

The dielectric function method (DFM), which uses a non-adiabatic approach to calculate the critical temperatures for superconductivity, has been quite successful in describing superconductors at low carrier densities. This regime of carrier densities causes other theories, such as BCS and Migdal-Eliashberg theory, to violate their assumption of a small Debye window. We investigate the application of DFM to the linear dispersion of single layer graphene. We derive the gap equation of DFM for a Dirac cone and calculate the critical temperature as a function of carrier density. This is done using an interaction potential that utilizes the Random Phase Approximation dielectric function and thus allows for plasmonic interactions. Our results show a significantly different behaviour of the critical temperature as a function of carrier density when compared to the BCS result. Thus, we find the DFM approach to be better suited when considering graphene systems at low carrier densities.

cond-mat.supr-con↗

arXiv2018

Dark soliton collisions in superfluid Fermi gases

In this work dark soliton collisions in a one-dimensional superfluid Fermi gas are studied across the BEC-BCS crossover by means of a recently developed finite-temperature effective field theory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015)] . The evolution of two counter-propagating solitons is simulated numerically based on the theory's nonlinear equation of motion for the pair field. The resulting collisions are observed to introduce a spatial shift into the trajectories of the solitons. The magnitude of this shift is calculated and studied in different conditions of temperature and spin-imbalance. When moving away from the BEC-regime, the collisions are found to become inelastic, emitting the lost energy in the form of small-amplitude density oscillations. This inelasticity is quantified and its behavior analyzed and compared to the results of other works. The dispersion relation of the density oscillations is calculated and is demonstrated to show a good agreement with the spectrum of collective excitations of the superfluid.

cond-mat.quant-gas↗

arXiv2015

Soliton core filling in superfluid Fermi gases with spin-imbalance

In this paper the properties of dark solitons in superfluid Fermi gases with spin-imbalance are studied by means of a recently developed effective field theory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015)] suitable to describe the BEC-BCS crossover in ultracold gases in an extended range of temperatures as compared to the usual Ginzburg-Landau treatments. The spatial profiles for the total density and for the density of the excess-spin component, and the changes of their properties across the BEC-BCS crossover are examined in different conditions of temperature and imbalance. The presence of population imbalance is shown to strongly affect the structure of the soliton excitation by filling its core with unpaired atoms. This in turn influences the dynamical properties of the soliton since the additional particles in the core have to be dragged along thus altering the effective mass.

cond-mat.quant-gas↗

arXiv2011

Resonant enhancement of the FFLO-state in 3D by a one-dimensional optical potential

We describe an imbalanced superfluid Fermi gas in three dimensions within the path-integral framework. To allow for the formation of the Fulde-Ferell-Larkin-Ovchinnikov-state (FFLO-state), a suitable form of the saddle-point is chosen, in which the pairs have a finite centre-of-mass momentum. To test the correctness of this path-integral description, the zero-temperature phase diagram for an imbalanced Fermi gas in three dimensions is calculated, and compared to recent theoretical results. Subsequently, we investigate two models that describe the effect of imposing a one-dimensional optical potential on the 3D imbalanced Fermi gas. We show that this 1D optical potential can greatly enlarge the stability region of the FFLO-state, relative to the case of the 3D Fermi gas without 1D periodic modulation. Furthermore it is show that there exists a direct connection between the centre-of-mass momentum of the FFLO-pairs and the wavevector of the optical potential. We propose that this concept can be used experimentally to resonantly enhance the stability region of the FFLO-state.

cond-mat.quant-gas↗