Anisotropic magneto-optical absorption and linear dichroism in two-dimensional semi-Dirac electron systems

Abstract

We present a theoretical study on the Landau levels (LLs) and magneto-optical absorption of a two-dimensional semi-Dirac electron system under a perpendicular magnetic field. Based on an effective k$\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{p}$ Hamiltonian, we find that the LLs are proportional to the two-thirds power law of the magnetic field and level index, which can be understood as a hybridization of the LL of Schr\"odinger and Dirac electrons with new features. With the help of the Kubo formula, we find the selection rule for interband (intraband) magneto-optical transition is anisotropic (isotropic). Specifically, the selection rules for interband magneto-optical transitions are $\mathrm{\ensuremath{\Delta}}n=0$, $\ifmmode\pm\else\textpm\fi{}2$ $(\ifmmode\pm\else\textpm\fi{}2,$ $\ifmmode\pm\else\textpm\fi{}4)$ for linearly polarized light along the linear (parabolic) dispersion direction, while the selection rules for the intraband transition are $\mathrm{\ensuremath{\Delta}}n=\ifmmode\pm\else\textpm\fi{}1,$ $\ifmmode\pm\else\textpm\fi{}3$ regardless of the polarization direction of the light. Further, the magneto-optical conductivity for interband (intraband) transition excited by linearly polarized light along the linear dispersion direction is two (one) orders of magnitude larger than that along the parabolic dispersion direction. This anisotropic magneto-optical absorption spectrum clearly reflects the structure of the LLs, and results in a strong linear dichroism. Importantly, a perfect linear dichroism with magnetic-field tunable wavelength can be achieved by using the interband transition between the two lowest LLs, i.e., from ${E}_{v0}$ to ${E}_{c0}$. Our results shed light on the magneto-optical property of the two-dimensional semi-Dirac electron systems and pave the way to design magnetically controlled optical devices.