Charge transport in two-dimensional system with massless Mexican-hat-like bands

Abstract

We study the single-particle, DC and optical properties of a two-dimensional (2D) system with massless Mexican-hat-like (W-shaped) valence bands. A proposed 2 × 2 Hamiltonian matrix gives the W-bands and two ground state phases: a gapped phase and a nodal-loop phase. The intraband properties include the single particle density of states, the effective concentration of charge carriers (the Drude weight), the Hall coefficient and electron mobility, electronic heat capacity and thermopower. The real part of the interband conductivity is calculated for the gapped phase as it depends on doping and temperature. As for the undoped nodal-loop phase only the zero-frequency interband conductivity is finite. Among several results two most decisively stand out: By measuring the Hall coefficient as a function of doping at zero-temperature we can answer whether the bands are W-shaped. By measuring the square-root singularity in the finite-temperature optical conductivity, we identify the gapped phase.