Search for Chiral Phonons in MnPS₃

Chiral phonons can be observed in two-dimensional transition metal dichalcogenide (TMDC) materials when the inversion symmetry is broken in the non-equilibrium state triggered by optical excitations using circularly polarized light. In order to avoid any debate about chirality in two dimensions, chiral phonons are henceforth refered to as circular phonons. A detailed theoretical calculation of the circular phonons production rate has already been done for the TMDC MoS₂ [1]. We investigate the antiferromagnetic semiconductor MnPS₃ with a similar band-structure like MoS₂ as a novel candidate material that may allow for excitation of circular phonons. In this material, although the total magnetic moment is zero in the ground state, exciting the system using circularly polarized light induces a net magnetic moment[2]. The damping of the magnetic moment observed experimentally points to the transfer of orbital angular moment to combined phonon-magnon excitations. We use DFT+U and density functional perturbation theory (DFPT) to search for circular phonon modes at the valley-points of a monolayer MnPS₃ and we obtain initial promising signatures for the same. We further perform calculations of the excited electronic states carrying orbital angular momentum with the help of the DFT+U and study the matrix elements for electron-phonon coupling in these states using DFPT, similar to the methodology recently employed for studying phonons in the 2D ferromagnet CrI₃ [3]. Our theoretical calculations could be used to design and bench-mark experiments on creation and detection of circular phonons using electronic and optical spectroscopy of valley polarization, time-resolved diffraction etc.

[1] Y. Pan and F. Caruso, Nano Lett. 23, 7463 (2023)
[2] M. Matthiesen, J. R. Hortensius, S. Manas Valero, I. Kapon, D. Dumcenco, E. Giannini, et al., Phys. Rev. Lett. 130, 076702 (2023)
[3] J. Bonini, S. Ren, D. Vanderbilt, M. Stengel, C. E. Dreyer, and S. Coh, Phys. Rev. Lett. 130, 086701 (2023)