  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.
