Orbital Angular Momentum Relaxation and Dephasing from First-Principles Density Matrix Dynamics

Orbitronics is a promising alternative to spintronics, due to advantages of using the orbital degree of freedom as the information carrier. Disentangling orbital angular momentum (OAM) responses from spin remains challenging experimentally and requires theoretical predictions and guidance for understanding the underlying physical mechanisms. We develop a first-principles density-matrix dynamics framework to study OAM relaxation and dephasing, explicitly including electron-electron and electron-phonon scatterings with spin-orbit coupling (SOC). We describe OAM within the modern theory of polarization, providing a complete description of both local and nonlocal contributions. This theoretical framework has been extensively validated for spin relaxation in disparate solids [1], and here is extended to orbital relaxation and transport.

We investigate orbital dynamics in both weak and strong SOC materials. For the strong SOC case, spin and orbital dynamics are closely coupled. For weak SOC materials, spin and OAM relax independently, and respond differently to the electric field. For increasing external electric field OAM relaxation becomes more D’yakonov–Perel’-like, while the opposite occurs for spin relaxation. This study provides insights for the electrical manipulation of OAM independently from spin, critical for the realization of next-generation orbitronic devices.

[1] J. Xu and Y. Ping, JCTC 20 2 (2023), ; J. Xu et al, Nat. Commun. 11, 2780, (2020), Nat. Commun. 15, 188, (2024)