Temperature Dependence of the Electronic Structure of TlInSe₂ and Spin–Orbit Coupling

Using high-resolution angle-resolved photoemission spectroscopy (ARPES), the electronic structure of the semiconductor TlInSe 2 is investigated across the reported structural phase transitions at 185 and 135 K. The ARPES intensity maps along the X-M, X-N′, and X/Γ-P/Z directions of the Brillouin zone (BZ) at 300, 160, and 30 K reveal that the valence band maxima (VBM) are located at the M and Z points of the BZ, such that at the Z point it has about 65 ± 10 meV higher binding energy than at the M point. A strong polarization effect is observed in TlInSe 2, suppressing the intensity at the VBM at the M point for horizontal polarization (P-pol) of light. A sizable spin–orbit (SO) splitting of the valence bands (VBs) is observed at the high symmetry points with absolute energies in good agreement with theoretical data based on density functional theory at the X, N′, and M points. The observed polarization effect and the SO splitting of the VBs based on ARPES have not been reported before. The experimental band structure data measured at different temperatures reveal that upon cooling, a band splitting develops between VBs, with no shift of the Fermi. The ARPES results support a three-dimensional electronic structure instead of quasi-one-dimensional behavior.