Vladimir Zhuravlev

2D massless Dirac Fermi gas model of superconductivity in the surface state of a topological insulator at high magnetic fields

The Nambu-Gorkov Greens function approach is applied to strongly type-II superconductivity in a 2D spin-momentum–locked (Weyl) Fermi gas model at high perpendicular magnetic fields. The resulting phase diagram can be mapped onto that derived for the standard, parabolic band-structure model, having the same Fermi surface parameters, E F and v , but with cyclotron effective mass . Significant deviations from the predicted mapping are found only for very small E F , when the Landau-Level filling factors are smaller than unity, and E F shrinks below the cutoff energy.

Discontinuous superconducting transitions in the paramagnetic limit: a non-perturbative approach

The unusual superconducting (SC) phase transitions occuring under competing orbital and spin pair breaking, which characterize clean strongly type-II superconductors at low temperatures, are investigated within a non-perturbative approach, which avoides the difficulties encountered in various perturbative approaches and enables comparison with recent experimental data. It is shown that in a 3D system with strong spin-splitting, a spatial (FFLO) modulation of the order parameter along the magnetic-field direction preserves the continuous nature of the SC transition. However, at a magnetic field slightly below Hc2 the FFLO state becomes unstable, transforming discontinuously into a uniform SC state via a first-order phase transition. Our calculation shows that the entropy jump at the first-order phase transition is siginificantly larger than its total variation in the continuous region between the two transitions, in agreement with recent thermal-conductivity measurements performed on the heavy-fermion compound URu2Si2.

Vortex Dynamics and Superconducting Fluctuation Effects on Magneto ‐ Oscillations in Extremely Type‐II Layered Superconductors

We study magneto‐oscillations in the vortex state of an extremely type‐II quasi 2D superconductor. It is argued that under the driving force generated by the sweeping magnetic field the superconductor tends to form 1D highly correlated channels of moving vortices, which reflect an underlying structure of easily sliding chains along the main principal axis in the Abrikosov vortex lattice. We present a model for calculating the friction coefficient of moving vortices in the presence of a dilute ensemble of strong pinning centers by exploiting the condition of minimal power dissipation. The model seems to account for the remarkable phenomenon of weak hysteresis loops, observed recently in magneto‐oscillations measurements far above the major irreversibility field of a nearly 2D organic superconductor.

Irreversible magnetization deep in the vortex-liquid state of a 2D superconductor at high magnetic fields

The remarkable phenomenon of weak magnetization hysteresis loops, observed recently deep in the vortex-liquid state of a nearly two-dimensional (2D) superconductor at low temperatures and high magnetic fields, is shown to reflect the existence of an unusual vortex-liquid state, consisting of collectively pinned crystallites of easily sliding vortex chains.

Vortex states in a two-dimensional superconductor at high magnetic field in a periodic pinning potential

The effect of a periodic pinning array on the vortex state in a 2D superconductor at low temperatures is studied within the framework of the Ginzburg-Landau approach. It is shown that attractive interaction of vortex cores to a commensurate pin lattice stabilizes vortex solid phases with long range positional order against violent shear fluctuations. Exploiting a simple analytical method, based on the Landau orbitals description, we derive a rather detailed picture of the low temperatures vortex state phase diagram. It is predicted that for sufficiently clean samples application of an artificial periodic pinning array would enable one to directly detect the intrinsic shear stiffness anisotropy characterizing the ideal vortex lattice.

Superconducting fluctuation effect on the de Haas–van Alphen oscillations in the vortex liquid state of quasi-2D superconductors

Abstract The damping of the de Haas–van Alphen (dHvA) oscillations in the mixed state of a 2D superconductor is studied within a new analytical approach to the problem of vortex-lattice fluctuations at high magnetic fields. It is shown that in the ‘liquid’ state around mean field H c2 ( T ), averaging over phase fluctuations leads to damping of the dHvA osillations, which can be well described by the random vortex lattice model. The calculated damping rate is in a good quantitative agreement with recent experiments carried out on a quasi-2D organic superconductor. It is predicted that deep in the mixed state, the freezing into an ordered vortex lattice is accompanied by a sharp upward turn in the slope of the ‘Dingle plot’.

A unified mean field approach to the dHvA effect in the vortex state near the upper critical field

The effect of nonmagnetic impurity scattering on the additional damping of de Haas-van Alphen (dHvA) oscillations in the mixed state of type II superconductors near the upper critical field is studied within mean field theory in the relaxation time approximation. Our calculations show that this effect becomes important only for small thermal smearing of the single particle distribution function and small disorder broadening of the Landau levels. The relationships between the different mechanisms of broadening are discussed.