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

Recently, a series of two-dimensional 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 nonunified conventions for pseudoangular momentum (PAM) in the previous studies. Here we use MoSi2As4 and MoS2 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 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.

Automated summary

Recently, there has been growing interest in a series of two-dimensional nonmagnetic layered materials called XSi2Y4 (where X represents transition metals and Y represents pnictogens) due to their potential applications. Similar to transition-metal dichalcogenides (TMDs), it is proposed that XSi2Y4 can exhibit chiral phonon involved valley-selective optical circular dichroism, which can be entangled with multiple Hall effects. However, comparing such effects between XSi2Y4 and TMDs has been challenging due to the lack of unified conventions for pseudoangular momentum (PAM) in previous studies. In this study, MoSi2As4 and MoS2 are used as examples to establish a unified convention for both phonon PAM and electronic PAM. The similarities and differences in crystal structure, band structures, and valley-selective optical circular dichroism between the two materials are also explored. The results show that in MoSi2As4, the chiral phonon emission/absorption, spin, valley, and transverse Hall current can be modulated by changing the energy or handedness of the incident light, demonstrating better performance than TMDs.