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arXiv · 2608.22838

Observation of current-induced orbital quadrupole accumulation

Geun-Hee Lee·Yubin Ji·Yongho Park·Changmin An·San Ko·Hye-Won Ko·Jinseob Lim·Jung Hyun Oh·Farzad Mahfouzi·Byong-Guk Park·Kab-Jin Kim·Mark D. Stiles·Kyoung-Whan Kim·Paul M. Haney·Kyung-Jin Lee
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Abstract

Spintronics and orbitronics rely on current-induced accumulations of magnetic dipoles: spin and orbital angular momentum. However, electronic orbitals inherently carry multipoles beyond the dipole, with the rank-2 orbital quadrupole as the leading term. Here we use polarization-resolved Kerr microscopy to observe current-induced orbital-quadrupole accumulation at the surfaces of Ti and Pt, metals with markedly different spin--orbit-coupling strengths. By separating the symmetric and antisymmetric components of the off-diagonal optical conductivity, we isolate the time-reversal-even quadrupolar response from the conventional time-reversal-odd magnetic-dipolar one, and find that the quadrupolar optical response exceeds the dipolar one in both metals. First-principles analysis of the measured responses indicates that the quadrupole accumulations are of the same order of magnitude in the two metals despite their widely different spin--orbit-coupling strengths, consistent with a previously unidentified channel of charge-to-orbital conversion that does not require spin--orbit coupling. Our findings establish that current-induced orbital polarization is fundamentally multipolar, expanding current-induced phenomena from the dipolar to the multipolar regime and opening a route to electrical control of orbital-ordered phases.

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Geun-Hee Lee, Yubin Ji, Yongho Park, Changmin An, San Ko, Hye-Won Ko, Jinseob Lim, Jung Hyun Oh, Farzad Mahfouzi, Byong-Guk Park, Kab-Jin Kim, Mark D. Stiles, Kyoung-Whan Kim, Paul M. Haney, Kyung-Jin Lee. 2026-08-24. Observation of current-induced orbital quadrupole accumulation. https://arxiv.org/abs/2608.22838

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