Phonon pseudoangular momentum in α-MoO₃

In recent studies, it has been discovered that phonons can carry angular momentum, leading to a series of investigations into systems with 3-fold rotation symmetry. However, for systems with 2-fold screw rotational symmetry, such as α-MoO₃, there has been no relevant discussion. In this paper, we investigated the pseudoangular momentum of phonons in crystals with 2-fold screw rotational symmetry. Taking α-MoO₃ as an example, we explain the selection rules in circularly polarized Raman experiments resulting from pseudoangular momentum conservation, providing important guidance for experiments. This study of pseudoangular momentum in α-MoO₃ opens up a new degree of freedom for its potential applications, expanding into new application domains.