A self-consistent Bogoliubov deGennes theory of the vortex lattice state in a 2D strong type-II superconductor at high magnetic fields reveals a novel quantum mixed state around the semiclassical Hc2, characterized by a well-defined Landau-Bloch band structure in the quasi-particle spectrum and suppressed order-parameter amplitude, which sharply crossover into the well-known semiclassical (Helfand-Werthamer) results upon decresing magnetic field. Application to the 2D superconducting state observed recently on the surface of the topological insulator Sb2Te3, accounts well for the experimental data, revealing a strong type-II superconductor, with unusualy low carrier density and very small cyclotron mass, which can be realized only in the strong coupling superconductor limit.PACS numbers: 74.25.Ha, 74.25.Uv The recent discoveries of surface and interface superconductivity with exceptionally high superconducting (SC) transition temperatures in several material struc- [3] promise to stimulate fundamental studies of the phenomenon of strong type-II superconductivity in two-dimensional (2D) and quasi 2D electron systems, particularly under high magnetic fields.[4] In a pure strong type-II superconductor under a uniform magnetic field the quasi particle spectrum is gapless in a broad field range below the upper critical field H c2 [5], [6], [4], where scattering of quasi particles by the vortex lattice interferes with the Landau quantization of the electron motion perpendicular to the magnetic field to form magnetic (Landau) Bloch's bands. In pure 2D, or quasi 2D, strong type-II SC systems, such as that realized in the multilayer system of the organic charge transfer salt κ − (ET ) 2 Cu (SCN ) 2 [7], under a magnetic field perpendicular to the easy conducting plane, the underlying normal electron spectrum is fully quantized and the effect of the vortex lattice is very pronounced. 2D vortex lattices can realize in such strongly layered electronic systems due to the presence of weak crystalline disorder [8], [9], where pinning of a few flux lines provide support for the entire vortex lattice against melting under an increasing magnetic field up to the irreversibility line [10]. Of special interest in the present paper is the unique situation of the 2D superconductivity realized in surface states of topological insulators, e.g. Due to the suppressed energy dispersion along the magnetic field direction, characterizing the 2D electron system, and the particle-hole symmetry inherent to the SC state, the quasi particle spectrum exhibits peculiar features that are missing in the 3D case. For example, at discrete magnetic field values where the chemical potential is located in the middle of a Landau band, so that the underlying normal state spectrum satisfies particle-hole symmetry, the calculated quasi-particle density of states shows a linear, Dirac-like energy dependence, which reflects topological singularities at the vortex lattice cores [4], [14]. Both the enhanced Landau quantization effect and the lucid reflection ...

Accurate magneto-optical determination of radius of topological nodal-ring Accurate magneto-optical determination of radius of topological nodal-ring semimetals semimetals

Weyl semimetals are a three dimensional topological phase of matter with linearly dispersed Weyl points which appear in pairs and carry opposite chirality. The separation of paired Weyl points allows charge transfer between them in the presence of parallel electric and magnetic fields, which is known as the chiral anomaly. In this paper, we theoretically study the influence of the chiral anomaly induced chiral charge imbalance on the Josephson current in a Weyl superconductor-Weyl semimetal-Weyl superconductor junction. In Weyl superconductors, two types of pairings are considered, namely, zero momentum BCS-like pairing and finite momentum FFLO-like pairing. For BCS-like pairing, we find that the Josephson current exhibits 0-π transitions and oscillates as a function of λ0L, where λ0 is the chirality imbalance induced by the parallel electric and magnetic fields and L is the length of the Weyl semimetal. The amplitude of the Josephson current also depends on the angle β between the line connecting two paired Weyl points and the transport direction along the junction. For FFLO-like pairing, the chirality imbalance induced periodic oscillations are absent and the Josephson current is also independent of the angle β. These findings are useful in detecting the chiral anomaly and distinguishing the superconducting pairing mechanism of Weyl semimetals.

Pairing-dependent superconductivity gap and nonholonomic Andreev reflection in Weyl semimetal/Weyl superconductor heterojunctions" (2018). Faculty of Engineering and Information Sciences -Papers: Part B. 1604. Pairing-dependent superconductivity gap and nonholonomic Andreev reflection in Pairing-dependent superconductivity gap and nonholonomic Andreev reflection in Weyl semimetal/Weyl superconductor heterojunctions Weyl semimetal/Weyl superconductor heterojunctions Abstract AbstractWe study superconductivity states mediated by the BCS and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairings in superconducting Weyl semimetals. It is found that a mixture of BCS and FFLO pairings results in a distinctive double-gap structure for superconducting states. With a heterojunction of a Weyl semimetal and a superconducting Weyl semimetal, we demonstrate the nonholonomic Andreev reflection and show that the intra-and internode Andreev reflections increase at the edges of the effective gap. The influence of interface potentials on the Andreev reflections is investigated. The conductance spectra arising from the mixed superconducting pairings is also analyzed. . Pairing-dependent superconductivity gap and nonholonomic Andreev reflection in Weyl semimetal/Weyl superconductor heterojunctions. PhysicalWe study superconductivity states mediated by the BCS and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairings in superconducting Weyl semimetals. It is found that a mixture of BCS and FFLO pairings results in a distinctive double-gap structure for superconducting states. With a heterojunction of a Weyl semimetal and a superconducting Weyl semimetal, we demonstrate the nonholonomic Andreev reflection and show that the intraand internode Andreev reflections increase at the edges of the effective gap. The influence of interface potentials on the Andreev reflections is investigated. The conductance spectra arising from the mixed superconducting pairings is also analyzed.

No abstract

The Nambu-Gorkov Green's function approach is applied to strongly type-II superconductivity in a 2D spin-momentum locked (Weyl) Fermi gas model at high perpendicular magnetic fields. When the chemical potential is sufficiently close to the branching (Dirac) point, such that the cyclotron effective mass, m * , is a very small fraction of the free electron mass, me, relatively large portion of the H − T phase diagram is exposed to magneto-quantum oscillation effects. This model system is realized in the 2D superconducting state, observed recently on the surface of the topological insulator Sb2Te3, for which high field measurements were reported at low carrier densities with m * = 0.065me. Calculations of the pairing condensation energy in such a system, as a function of H and T , using both the Weyl model and a reference standard model, that exploits a simple quadratic dispersion law, are found to yield indistinguishable results in comparison with the experimental data. Significant deviations from the predictions of the standard model are found only for very small carrier densities, when the cyclotron energy becomes very large, the Landau level filling factors are smaller than unity, and the Fermi energy shrinks below the cutoff energy. PACS numbers: 74.78.-w, 74.25.Ha, 74.20.-z Expanding the above normal state Green's functions in terms of the complete set of solutions, ϕ n (y − k x ) =

Thermoelectric and thermal transport properties of graphene under strong Thermoelectric and thermal transport properties of graphene under strong magnetic field magnetic field

We present a qualitative and quantitative study of magneto-thermoelectric effect of graphene. In the limit of impurity scattering length being much longer than the lattice constant, the intra-valley scattering dominates the charge and thermal transport. The self-energy and the Green's functions are calculated in the self-consistent Born approximation. It is found that the longitudinal thermal conductivity splits into double peaks at high Landau levels and exhibits oscillations which are out of phase with the electric conductivity. The chemical potential dependent electrical resistivity, the thermal conductivities, the Seebeck coefficient, and the Nernst coefficient have been obtained. The results are in good agreement with the experimental observations.