Understanding mechanisms of orbital relaxation and Rashba effect Pohang University of Science and Technology

Abstract

The field of orbitronics encompasses various phenomena related to the genera- tion and utilization of orbital currents electrically. Although it has been traditionally believed that orbital currents are quenched quickly due to interactions with the crystal field, recent developments such as the orbital Hall effect and the orbital Rashba effect have enabled the efficient generation of orbital currents, bringing significant attention to orbitronics. One of the most pressing issues in orbitronics is the rapid quenching of orbital currents within solids due to the crystal field and frequent collisions with numer- ous impurities. Fortunately, recent experiments have revealed that orbital currents can persist for a long time despite the crystal field and collisions with many impuri- ties, prompting extensive theoretical research into the mechanisms that allow for their longevity. My research focuses on the theoretical understanding of how orbital currents can persist despite numerous collisions with impurities in a solid. For spin currents, it has been established that the Dyakonov-Perel (DP) mechanism, which is typically coun- terintuitive, can cause collisions with impurities to impede the decay of spin currents. However, the DP mechanism traditionally requires broken inversion symmetry, mak- ing it challenging to apply to materials where orbital currents are commonly studied due to their inversion symmetry. My findings reveal that for orbital currents, the DP mechanism can operate even in the presence of inversion symmetry, distinguishing it from spin currents. Fur- thermore, when spin-orbit coupling is present, linking orbital currents with spin cur- rents, the decay of spin currents can also be explained by the DP mechanism even in inversion-symmetric systems. This discovery challenges the conventional belief that the DP mechanism is inapplicable to spin current decay in inversion-symmetric systems, showing that it is indeed possible.