arXiv subjects

M. A. Griffith

Publications and source records attributed to M. A. Griffith.

3 recordsLinked to original sources

arXiv2019

Kramers' doublet ground state in topological Kondo insulators

We consider the simplest variant of a Kondo insulator where a doublet of localized $f$-electrons hybridizes with spin-degenerate conduction electrons. We analyse the symmetries of $f$-orbitals involved in the hybridization and point out that the effective four-band model of such systems is adiabatically connected with one that possesses chiral symmetry, which provides further descriptions of clean Kondo insulators. We obtain general conditions for the appearance of topological non-trivial states and discuss implications for rare-earth based compounds. As an example, we derive the full phase diagram of tetragonal Kondo insulators. We show that the chiral symmetry leads to a non-trivial topological phase when the band-width of conduction electrons sets the largest energy scale, and a new weak topological phase appears as function of the normalized distance between bands' centers.

cond-mat.str-el↗

arXiv2017

Multiband superconductivity in ${\rm BiS_2}$-based layered compounds

A mean-field treatment is presented of a square lattice two-orbital-model for ${\rm BiS_2}$ taking into account intra- and inter-orbital superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between the couplings of electrons in the same and different orbitals (${\rm η= V_{XX}/V_{XY}}$) and electron doping $x$. With the help of a quantity we call orbital-mixing ratio, denoted as $R(ϕ)$, the phase diagram is analyzed using a simple and intuitive picture based on how $R(ϕ)$ varies as electron doping increases. The predictive power of $R(ϕ)$ suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.

cond-mat.supr-con↗

arXiv2015

Applying experimental constraints to a one-dimensional model for BiS2 superconductivity

Recent ARPES measurements [Phys. Rev. B 92, 041113 (2015)] have confirmed the one-dimensional character of the electronic structure of CeO0.5F0.5BiS2, a representative of BiS2-based superconductors. In addition, several members of this family present sizable increase in the superconducting transition temperature Tc under application of hydrostatic pressure. Motivated by these two results, we propose a one-dimensional three-orbital model, whose kinetic energy part, obtained through ab initio calculations, is supplemented by pair-scattering terms, which are treated at the mean-field level. We solve the gap equations self-consistently and then systematically probe which combination of pair-scattering terms gives results consistent with experiment, namely, a superconducting dome with a maximum Tc at the right chemical potential and a sizable increase in Tc when the magnitude of the hoppings is increased. For these constraints to be satisfied multi-gap superconductivity is required, in agreement with experiments, and one of the hoppings has a dominant influence over the increase of Tc with pressure.

cond-mat.supr-con↗