Microscopic Theory of Chiral-Phonon-Induced Orbital Selectivity in Helical Crystals

Abstract

We present a microscopic theory of chirality-induced orbital selectivity (CIOS) in helical crystals, in which truly chiral phonons selectively transfer angular momentum to electronic orbital degrees of freedom. For a threefold helical crystal with line-group symmetry $L{3}_1$, we show that phonon-induced local rotations generate a rotational electron-phonon interaction proportional to ${\hat{L}}^{\pm }$, which drives the orbital transfer $m_{\ell }\to m_{\ell }-m_s$ in accordance with crystal angular momentum (CAM) conservation, where $m_s=\pm 1$ denotes the eigenvalue of the phonon rotational mode. Evaluating $⟨{\hat{L}}^z⟩$ to leading order in perturbation theory, we find that the orbital response is suppressed near the $\hat{I}“$ point and the BZ boundary, and enhanced at intermediate wave vectors -- a feature intimately tied to the degeneracy structure of the phonon bands.

5 pages, 3 figures