MBE growth of magnetic TI heterostructures

The magnetic TI films and heterostructures were grown on heat-treated 0.5-mm-thick insulating SrTiO₃(111) substrates using two MBE chambers (Omicron Lab 10 and Vecco Applied EPI 620) with a base pressure of 2.0 × 10⁻¹⁰ mbar. Prior to sample growth, the SrTiO₃ substrates are first degassed at ~600 °C for 1 h. High-purity Sb(6N), Te(6N), V(5N), and Cr(5N) are evaporated from Knudsen cells. During the growth of the magnetic TI films, the substrate is maintained at ~240 °C. The flux ratio of Te/(Sb + V/Cr) is set to be >10 to avoid possible Te deficiency in samples. The growth rate of magnetic TI or TI films is around ~0.2 QL/min. Finally, the samples are capped with a 10 nm Te layer to prevent their degradation during the ex situ electrical transport measurements. The V concentration in V-doped Sb₂Te₃ films is tuned by adjusting the temperature of the V effusion cell. The x = 0.08–0.2 samples correspond to the V cell temperatures from 1440 to 1490 °C. For the Sb_1.84Cr_0.16Te₃ sample, the temperature of the Cr effusion cell is 1160 °C. The Cr and V concentration values in this work are calibrated by the plot in our prior work¹².