Chiral phonons entangled with multiple Hall effects and unified convention for pseudoangular momentum in two-dimensional materials

Abstract

Recently, a series of two-dimensional nonmagnetic layered materials $X{\mathrm{Si}}_{2}{Y}_{4}$ ($X$=transition metals; $Y$ = pnictogens) having similar crystal structures with transition-metal dichalcogenides (TMDs) were proposed for their potential application value. Like TMDs, we propose that chiral phonon involved valley-selective optical circular dichroism can be also obtained in $X{\mathrm{Si}}_{2}{Y}_{4}$, and it can be further entangled with multiple Hall effects. However, it is difficult to compare such effect between $X{\mathrm{Si}}_{2}{Y}_{4}$ and TMDs due to the nonunified conventions for pseudoangular momentum (PAM) in the previous studies. Here we use ${\mathrm{MoSi}}_{2}{\mathrm{As}}_{4}$ and ${\mathrm{MoS}}_{2}$ as examples to establish a unified convention for both phonon PAM and electronic PAM, together with showing their similarities and differences in crystal structure, band structures, and valley-selective optical circular dichroism. In particular, we find in ${\mathrm{MoSi}}_{2}{\mathrm{As}}_{4}$, the chiral phonon emission/absorption, the spin, the valley, and the transverse Hall current, can be modulated by changing either the energy or the handedness of the incident light, which show better performance than TMDs.