Chiral phonons entangled with multiple Hall effects and unified convention for pseudoangular momentum in 2D materials

TL;DR

This paper introduces a unified convention for pseudo-angular momentum in 2D materials, demonstrating chiral phonons entangled with Hall effects and enhanced valley-selective optical properties in XSi2Y4 compounds compared to TMDs.

Contribution

It establishes a unified framework for phonon and electronic pseudo-angular momentum in 2D materials, enabling better comparison and understanding of their optical and Hall effects.

Findings

Chiral phonons in XSi2Y4 can be modulated by light energy and handedness.

XSi2Y4 show improved performance in Hall effects compared to TMDs.

Unified convention clarifies differences and similarities in valley-selective phenomena.

Abstract

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.