Mihail Silaev

Microscopic Theory of Type-1.5 Superconductivity in Multiband Systems

We report a self-consistent microscopic theory of characteristic length scales, vortex structure, and type-1.5 superconducting state in two-band systems using two-band Eilenberger formalism.

Microscopic Derivation of Two-Component Ginzburg-Landau Model and Conditions of its Applicability in Two-Band Systems

We report a microscopic derivation of two-component Ginzburg-Landau (GL) field theory and the conditions of its validity in two-band superconductors. We also investigate the conditions when microsc ...

Type-1.5 superconductivity in multiband systems: Magnetic response, broken symmetries and microscopic theory – A brief overview

Abstract A conventional superconductor is described by a single complex order parameter field which has two fundamental length scales, the magnetic field penetration depth λ and the coherence length ξ . Their ratio κ determines the response of a superconductor to an external field, sorting them into two categories as follows; type-I when κ 1 / 2 and type-II when κ > 1 / 2 . We overview here multicomponent systems which can possess three or more fundamental length scales and allow a separate “type-1.5” superconducting state when, e.g. in two-component case ξ 1 2 λ ξ 2 . In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges. As a consequence the system should form an additional Semi-Meissner state which properties we discuss below. In that state vortices form clusters in low magnetic fields. Inside the cluster one of the component is depleted and the superconductor-to-normal interface has negative energy. In contrast the current in second component is mostly concentrated on the cluster’s boundary, making the energy of this interface positive. Here we briefly overview recent developments in Ginzburg–Landau and microscopic descriptions of this state.

Long-Range Spin Accumulation from Heat Injection in Mesoscopic Superconductors with Zeeman Splitting

We describe far-from-equilibrium nonlocal transport in a diffusive superconducting wire with a Zeeman splitting, taking into account different spin relaxation mechanisms. We demonstrate that due to the Zeeman splitting, an injection of current in a superconducting wire creates spin accumulation that can only relax via thermalization. This effect leads to a long-range spin accumulation detectable in the nonlocal signal. Our model gives a qualitative explanation and provides accurate fits of recent experimental results in terms of realistic parameters.

Stable fractional flux vortices and unconventional magnetic state in two-component superconductors

In the framework of London theory we study the unconventional magnetic state in two-component superconductors with a finite density of fractional flux vortices stabilized near the surface. We show that the process of vortex entry into the two-component superconductor consists of several steps, while the external magnetic field increases from zero. At the first stage only vortices in one of the order parameter components penetrate and sit at the equilibrium position near the surface. When the magnetic field is increased further, vortices in the second-order parameter component eventually enter the superconductor. Such a complex partial vortex penetration leads to the modification of a Bean-Livingston barrier and a magnetization curve as compared to conventional single-component superconductors. We discuss the possibility of experimental identification of protonic superconductivity in the projected superconducting state of liquid metallic hydrogen and hydrogen-rich alloys with the help of the partial vortex penetration effect.

Universal Mechanism of Dissipation in Fermi Superfluids at Ultralow Temperatures

We show that the vortex dynamics in Fermi superfluids at ultralow temperatures is governed by the local heating of the vortex cores creating the heat flux carried by nonequilibrium quasiparticles emitted by moving vortices. This mechanism provides a universal zero temperature limit of dissipation in Fermi superfluids. For the typical experimental conditions realized by the turbulent motion of ^{3}He-B, the temperature of the vortex cores is estimated to be of the order 0.2 T(c). The dispersion of Kelvin waves is derived, and the heat flow generated by Kelvin cascade is shown to have a value close to that experimentally observed.

Lifshitz Transition in the Double-Core Vortex in ^{3}He-B.

We study the spectrum of fermion states localized within the vortex core of a weak-coupling p-wave superfluid. The low energy spectrum consists of two anomalous branches that generate a large density of states at the locations of the half cores of the vortex. Fermi liquid interactions significantly stretch the vortex structure, which leads to a Lifshitz transition in the effective Fermi surface of the vortex core fermions. We apply the results to the rotational dynamics of vortices in superfluid ^{3}He-B and find an explanation for the observed slow mode.

Lindblad-equation approach for the full counting statistics of work and heat in driven quantum systems

We formulate the general approach based on the Lindblad equation to calculate the full counting statistics of work and heat produced by driven quantum systems weakly coupled with a Markovian thermal bath. The approach can be applied to a wide class of dissipative quantum systems driven by an arbitrary force protocol. We show the validity of general fluctuation relations and consider several generic examples. The possibilities of using calorimetric measurements to test the presence of coherence and entanglement in the open quantum systems are discussed.

Unconventional thermoelectric effect in superconductors that break time-reversal symmetry

We demonstrate that superconductors that break time-reversal symmetry can exhibit thermoelectric properties, which are entirely different from the Ginzburg mechanism. As an example, we show that in the s + is superconducting state there is a reversible contribution to thermally induced supercurrent, whose direction is not invariant under time-reversal operation. Moreover in contrast to Ginzburg mechanism it has a singular behavior near the time-reversal symmetry breaking phase transition. The effect can be used to confirm or rule out the s + is state, which is widely expected to be realized in pnictide compounds Ba1-xKxFe2As2 and stoichiometric LiFeAs.

Unusual Mechanism of Vortex Viscosity Generated by Mixed Normal Modes in Superconductors with Broken Time Reversal Symmetry

We show that under certain conditions, multiband superconductors with broken time reversal symmetry have a vortex viscosity-generating mechanism which is different from that in conventional superco ...