Orbital-quadrupole explanation of long orbital relaxation lengths

Determine whether orbital-quadrupole accumulation, which has symmetries distinct from orbital angular momentum, explains the long orbital relaxation lengths observed in several experiments despite theoretical predictions of very short orbital-angular-momentum relaxation lengths.

Background

The paper reports that current-induced orbital-quadrupole accumulation is substantial and can dominate the optical response in Ti and Pt. This finding motivates reconsidering the interpretation of current-driven torques and orbital relaxation phenomena, which have traditionally focused primarily on orbital angular momentum accumulation.

The authors note a discrepancy between relatively long orbital relaxation lengths measured in several experiments and theoretical predictions of very short orbital-angular-momentum relaxation lengths. Because orbital quadrupoles have different symmetries from orbital angular momentum, the paper identifies determining whether quadrupolar accumulation accounts for this discrepancy as an unresolved problem.

References

Whether the orbital quadrupole, which has different symmetries from OAM, explains the observations remains an open question.

— Observation of current-induced orbital quadrupole accumulation  (2608.22838 - Lee et al., 24 Aug 2026) in Section “Discussion and outlook”