arXiv subjects

Mir Vahid Hosseini

Publications and source records attributed to Mir Vahid Hosseini.

24 records · Page 2Linked to original sources

arXiv2016

Inhomogeneous superconductivity in the presence of time-reversal symmetry

We propose a new type of non-uniform condensate state in the presence of time-reversal symmetry. The underlying platform of this state is a corrugated honeycomb lattice which exhibits an inhomogeneous pseudo magnetic field. Using the self-consistent tight-binding Bogoliubov-de Gennes formalism, we show that an s-wave pairing of chiral carriers in the presence of an inhomogeneous pseudo magnetic field results in a spatially modulated order parameter with the half wavelength of the corrugation. The manner of modulation depends on the fundamental directions of the honeycomb lattice, the zigzag and armchair directions. The stability of this inhomogeneous superconductivity is also analyzed and possible experimental realization is discussed.

cond-mat.supr-con↗

arXiv2016

Ruderman-Kittel-Kasuya-Yosida interaction in Weyl semimetals

We theoretically demonstrate the Ruderman-Kittel-Kasuya-Yosida interaction between magnetic impurities that is mediated by the Weyl fermions embedded inside a three-dimensional Weyl semimetal (WSM). The WSM is characterized by a pair of Weyl points separated in the momentum space. Using the Green's function method and a two-band model, we show that four terms contribute to the magnetic impurity interaction in the WSM phase: the Heisenberg, Dzyaloshinsky-Moriya, spin-frustrated and Ising terms. Except the last term which is vanishingly small in the plane perpendicular to the line connecting two Weyl points, all the other interaction terms are finite. Furthermore, the magnetic spins of the Dzyaloshinsky-Moriya and spin-frustrated terms lie in the plane perpendicular to the line connecting two Weyl points, but in this plane, the magnetic spins of the Ising term have no components. For each contribution, an analytical expression is obtained, falling off with a spatial dependence as $R^{-5}$ at Weyl points and showing beating behavior that depends on the direction between two magnetic impurities.

cond-mat.mes-hall↗

arXiv2016

Quantum Transport of Dirac fermions in graphene with a spatially varying Rashba spin-orbit coupling

We theoretically study electronic transport through a region with inhomogeneous Rashba spin-orbit (RSO) coupling placed between two normal regions in a monolayer graphene. The inhomogeneous RSO region is characterized by linearly varying RSO strength within its borders and constant RSO strength in the central region. We calculate the transmission properties within the transfer matrix approach. It is shown that the amplitude of conductance oscillations reduces and at the same time the magnitude of conductance increases with increasing border thickness. We also investigate how the Fano factor can be modified by the border thickness of RSO region.

cond-mat.mes-hall↗

arXiv2012

Unconventional superconducting states of interlayer pairing in bilayer and trilayer graphene

We develop a theory for interlayer pairing of chiral electrons in graphene materials which results in an unconventional superconducting (S) state with s-wave spin-triplet order parameter. In a pure bilayer graphene, this superconductivity exhibits a gapless property with an exotic effect of temperature-induced condensation causing an increase of the pairing amplitude (PA) with increasing temperature. We find that a finite doping opens a gap in the excitation spectrum and weakens this anomalous temperature-dependence. We further explore the possibility of realizing variety of pairing patterns with different topologies of the Fermi surface, by tuning the difference in the doping of the two layers. In trillayer graphene, the interlayer superconductivity is characterized by a two components order parameter which can be used to define two distinct phases in which only one of the components is non vanishing. For ABA stacking the stable state is determined by a competition between these two phases. By varying the relative amplitude of the corresponding coupling strenghes, a first order phase transition can occur between these two phases. For ABC stacking, we find that the two phases coexist with a possibility of a similar phase transition which turns out to be second order.

cond-mat.mes-hall↗

arXiv2012

Relativistic model for electron-hole pairing in the superconducting state of graphene-based materials

We propose a graphene-based model for realizing a new type of gapless condensate by pairing of electron-like (n) carriers of a Dirac cone conduction band with hole-like (p) carriers of a Dirac valance band. Ferromagnetic superconductivity (FS) in monolayer graphene or pairing between oppositely (n and p) doped layers of a double layer graphene allow for the formation of this p-n superconductivity. For FS in graphene, the p-n condensate dominates the zero temperature phase diagram at low levels of doping and high exchange fields. We show that p-n pairing with p+ip-wave symmetry presents a stable condensate phase, which can cover the phase diagram up to surprisingly strong exchange fields. Our study reveals that the characteristics of relativistic quantum physics affect the interplay between ferromagnetic ordering and superconductivity in a fundamental way.

cond-mat.mes-hall↗

arXiv2012

Model of an exotic chiral superconducting phase in a graphene bilayer

We theoretically demonstrate the formation of a new type of unconventional superconductivity in graphene materials, which exhibits gapless property. The studied superconductivity is based on an interlayer pairing of chiral electrons in bilayer graphene, which results in an exotic s-wave spin-triplet condensate order with anomalous thermodynamic properties. These include the possibility of a temperature induced condensation causing an increase of the pairing gap with increasing temperature, and an entropy of the stable superconducting state which can be higher than its value in the normal state. Our study reveals the analogy of the interlayer superconductivity in graphene materials to the color superconductivity in dense quark matter and the gapless pairing states in nuclear matter and ultra-cold atomic gases.

cond-mat.mes-hall↗