Hidden spin-orbital texture at the $\bar{\Gamma}$-located valence band maximum of a transition metal dichalcogenide semiconductor

TL;DR

This study reveals a hidden, layer-specific spin texture in the valence bands of 1T-HfSe₂, driven by local electric dipoles and orbital contributions, with implications for spintronics and optoelectronic applications.

Contribution

It uncovers a ground-state, layer-confined spin texture in a transition metal dichalcogenide, controlled by light polarization, advancing understanding of spin-polarization mechanisms without magnetism.

Findings

Layer-specific spin polarization confined within Se-sublayers.

Spin-orbital textures obey time-reversal symmetry but show local TRS-breaking features.

Spin polarization can be tuned by linear light polarization.

Abstract

Finding stimuli capable of driving an imbalance of spin-polarised electrons within a solid is the central challenge in the development of spintronic devices. However, without the aid of magnetism, routes towards this goal are highly constrained with only a few suitable pairings of compounds and driving mechanisms found to date. Here, through spin- and angle-resolved photoemission along with density functional theory, we establish how the $p$-derived bulk valence bands of semiconducting 1T-HfSe$_2$ possess a local, ground-state spin texture spatially confined within each Se-sublayer due to strong sublayer-localised electric dipoles orientated along the $c$-axis. This hidden spin-polarisation manifests in a `coupled spin-orbital texture' with in-equivalent contributions from the constituent $p$-orbitals. While the overall spin-orbital texture for each Se sublayer is in strict adherence to time-reversal symmetry (TRS), spin-orbital mixing terms with net polarisations at time-reversal invariant momenta are locally maintained. These apparent TRS-breaking contributions dominate, and can be selectively tuned between with a choice of linear light polarisation, facilitating the observation of pronounced spin-polarisations at the Brillouin zone centre for all $k_z$. We discuss the implications for the generation of spin-polarised populations from 1T-structured transition metal dichalcogenides using a fixed energy, linearly polarised light source.