Hidden orbital polarization in diamond, silicon, germanium, gallium arsenide and layered materials

TL;DR

This paper reveals the widespread presence and fundamental importance of hidden orbital polarization in various materials, expanding the understanding of spintronics beyond spin-based effects and suggesting new experimental and technological implications.

Contribution

It introduces a universal framework for analyzing hidden orbital polarization, demonstrating its abundance, independence from spin-orbit coupling, and significance in antiferromagnetic applications.

Findings

Hidden orbital polarization exists even without spin-orbit coupling.

Compression significantly reduces hidden spin polarization in transition metal dichalcogenides.

Current-induced hidden orbital polarization can influence antiferromagnetic states.

Abstract

It was previously believed that the Bloch electronic states of non-magnetic materials with inversion symmetry cannot have finite spin polarizations. However, since the seminal work by Zhang et al. [Nat. Phys. 10, 387-393 (2014)] on local spin polarizations of Bloch states in non-magnetic, centrosymmetric materials, the scope of spintronics has been significantly broadened. Here, we show, using a framework that is universally applicable independent of whether hidden spin polarizations are small (e.g., diamond, Si, Ge, and GaAs) or large (e.g., MoS2 and WSe2), that the corresponding quantity arising from orbital - instead of spin - degrees of freedom, the hidden orbital polarization, is (i) much more abundant in nature since it exists even without spin-orbit coupling and (ii) more fundamental since the interband matrix elements of the site-dependent orbital angular momentum operator determines the hidden spin polarization. We predict that the hidden spin polarization of transition metal dichalcogenides is reduced significantly upon compression. We suggest experimental signatures of hidden orbital polarization from photoemission spectroscopies and demonstrate that the current-induced hidden orbital polarization may play a far more important role than its spin counterpart in antiferromagnetic information technology by calculating the current-driven antiferromagnetism in compressed silicon.