Effect of electron-hole asymmetry on optical conductivity in 8-Pmmn borophene

Abstract

8-Pmmn borophene is a polymorph of borophene that exhibits anisotropic tilted Dirac cones. In our work, we have done a detailed theoretical study of the optical conductivity of 8-Pmmn borophene. We provide exact analytical expressions of the maximum optical conductivity. We also obtain exact analytical expressions of the minimum energy (1) required to trigger the inter-band optical transitions and energy (2) needed to attain maximum optical conductivity. We find that the optical conductivity are highly anisotropic as a consequence of the anisotropic Dirac cone. The optical conductivities have a non-monotonic behavior with photon energy in the regime between 1 and 2, as a result of the tilted parameter . The tilted parameter can be extracted by knowing 1 and 2 from optical measurements.

The maximum values of the components of the optical conductivity do notdepend on the carrier density and the tilted parameter. The product of the maximum values of the anisotropic conductivities has the universal value (e2=4h2 ). The tilted anisotropic Dirac cones in 8-Pmmn borophene can be realized by the optical conductivity measurement.

Reference: S.Verma, A. Mawrie and T. K. Ghosh, Physical Review B 96, 155418 (2017).