Extra Seminar - Würzburg ToCoTronics Colloquium

The orbital magnetization, rooted in the orbital angular momentum (OAM) of Bloch electrons, is a fundamental observable deeply intertwined with the geometry of quantum states. Historically considered secondary to spin, OAM is now recognized as a critical quantity underpinning orbital transport phenomena. The quantum geometric tensor (QGT)—comprising the quantum metric and Berry curvature—is intimately connected to this magnetization, as the intrinsic OAM serves as the physical observable corresponding to the imaginary part of the geometry (Berry curvature).

In this talk, I will first present a framework to probe this orbital magnetization using circular dichroism ARPES. By mapping the OAM texture and the band curvature in detail, we demonstrate the reconstruction of the full QGT in the kagome metal CoSn, quantifying the non-trivial geometry of its topological flat bands [1]. Second, I will discuss how OAM textures manifest in chiral systems. Focusing on the chiral crystal (TaSe₄)₂I, we visualize a novel p-wave OAM texture—a dipolar pattern locked to the lattice chirality that vastly exceeds the spin polarization [2]. These findings collectively establish OAM as a primary, manipulable degree of freedom, bridging fundamental band topology with the emerging field of "spinless orbitronics" [3].

[1] M. Kang, et al., Measurements of the quantum geometric tensor in solids, Nature Physics 21, 110 (2025).
[2] D. Oh, et al., p-wave orbital angular momentum texture in a chiral crystal, under review (2025).
[3] D. Oh, et al., Interplay of orbital angular momentum and chirality, Nature Physics (2025). DOI:10.1038/s41567-025-03113-2