Quantum Hall effect and magnetic topological phase transition in ultra-low carrier density Sb₂Te₃ films

In 2014, the quantum Hall effect (QHE) originated from topological surface states (TSS) was observed for back-gated BiSbTeSe₂ single-crystal and shortly after for back-gated MBE-grown (Bi_1−xSb_x)₂Te₃ films. A year later, with the aid of proper insulating buffer-layer as a growth template along with novel growth methodology, we reported TSS-originated QHE in large area defect-suppressed MBE-grown Bi₂Se₃ films (sheet carrier density as low as ~7×10¹¹ /cm²) with vanishing longitudinal resistance in absence of gating and without adding impurity. However, for all aforementioned cases, a high magnetic field was required to observe the QHE phenomena. Extending the buffer- layer scheme to telluride system allowed us to achieve Sb₂Te₃ thin films with even lower defect density (carrier density as low as ~1.5×10¹¹ /cm²) which eventually led to observation of QHE (without application of gating) at much lower magnetic field of ~5T which is ~5 times lower than the required field for observing QHE in pure binary selenide system of Bi₂Se₃. Moreover, these samples demonstrate topological phase transition under higher magnetic fields. In this talk, I will discuss the growth procedure and novel magneto-transport properties of these ultra-low defect-density Sb₂Te₃ films.