Optical conductivity and polarization rotation of type-II semi-Dirac materials
Qing-Yun Xiong, Jia-Yan Ba, Hou-Jian Duan, Ming-Xun Deng, Yimin Wang, Rui‐Qiang Wang
Abstract
The semi-Dirac point of type-II semi-Dirac (SD) materials is a merging of triple Dirac points, distinguishing from the conventional type-I SD with double-Dirac point merging, and exhibits unique topological property. Here, we investigate its longitudinal and transverse optical conductivities. By controlling the evolution of the SD point with a perturbation parameter $\mathrm{\ensuremath{\Delta}}$, we present large longitudinal optical conductivity at the Van Hove singularity, not only in linear but also in parabolic directions. Furthermore, we find the nonzero dynamical Hall conductivity, which is sensitive to the Fermi energy and Dirac mass. Through introducing a momentum-dependent mass term, e.g., irradiating with circularly polarized light, the dynamical Hall conductivity exhibits more featured structures, depending on the parameter $\mathrm{\ensuremath{\Delta}}$, due to opening new channels of interband transitions. It is found that the frequency-dependent Kerr/Faraday angle can present all features of the dynamical Hall conductivity at characteristic frequencies. By detecting the Kerr or Faraday spectra, it is helpful to understand the physics of evolution of the SD to Dirac regime and further to extract the systemic parameters of SD materials from characteristic frequencies.