Orbital angular momentum dynamics in nonequilibrium condensed matters(Speaker: Kyoung-Whan Kim)*

Roles of orbital angular momentum of electrons in solids have been ignored for a long time because of the orbital quenching. However, recent theoretical and experimental reports imply that orbital angular momentum is not quenched in nonequilibrium. Furthermore, it is claimed that the orbital degree of freedom is crucial for anomalous spin transport phenomena such as the spin Hall effect. Therefore, understanding the dynamics of orbital angular momentum has become important in the aspect of both fundamental science and spintronic applications. However, it has been believed that the dynamics of orbital angular momentum and that of spin angular momentum are qualitatively similar, so the experimental characterization of orbital dynamics requires quantitative analysis, which is difficult in general.

In this talk, I would like to point out a qualitative difference between the orbital and spin angular momenta by revealing a hidden degree of freedom of the orbital angular momentum, which is named the orbital angular position. It mediates the oscillation of the orbital angular momentum even without breaking time-reversal or spatial-inversion symmetry, which is impossible for spin. Our quantum Boltzmann approach indicates that considering the orbital angular position is essential for the theoretical description of orbital transport. Also, I would like to propose several experimental methods to measure the distinct dynamics of orbital angular momentum.