Evolution of the band structure of α-Sn(001) thin film on InSb(001)

Determining the topological phase of a material is a popular research route in condensed matter physics. For elemental material of α-Sn, its topological phase has been under debate. α-Sn(001) with in-plane compressive strain is expect to be a topological Dirac semimetal in theory, but experimental evidence of 3D Dirac state is still lacking. In contrast, a spin-momentum locked topological surface state (TSS) was found for α-Sn(001) on InSb(001), suggesting a topological insulator (TI). In this work, molecular beam epitaxy grown α-Sn(001) on InSb(001) and the thickness dependent angle-resolved photoemission spectroscopy (ARPES) study from 3 bilayers (BLs) to 370 BLs are reported. Streaky (2×1) reflection high energy electron diffraction patterns and narrowθ-rocking curve (FWHM of 0.0163°) in x-ray diffraction indicated an excellent crystallinity. Sharp TSSs were attained by ARPES in films thicker than 6 BLs without resorting to extra doping or surface treatments. No TSSs were observed for film thinner than 5 BLs, indicating a crossover from 3D TI to trivial insulator. In an extremely thick α-Sn film of 370 BLs, no evident k_z dependence on the Dirac state was found in photon energy range of 10-40 eV, suggesting α-Sn(001) on InSb(001) more likely to be in TI phase.