  Recently, a series of two-dimensional (2D) nonmagnetic layered materials
XSi2Y4 (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 XSi2Y4, and
it can be further entangled with multiple Hall effects. However, it is
difficult to compare such effect between XSi2Y4 and TMDs due to the non-unified
conventions for pseudo-angular momentum (PAM) in the previous studies. Here we
use MoSi2As4 and MoS2 as examples to establish 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 MoSi2As4, 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.
