Structural Phase Transition and Carrier Density Tuning in SnSexTe1-x Nanoplates for Topological Crystalline Insulators

Abstract

For topological insulators and topological crystalline insulators (TCIs), their exotic surface states are promising for fundamental condensed matter physics research as well as future electronics such as low-dissipation electronics and spintronics. However, the high bulk carrier density that often dominates the transport property is the major materials challenge, critically hindering our ability to study and manipulate the surface states. In this manuscript, we demonstrate an alloying strategy, SnSexTe1-x, to effectively reduce the bulk carrier density. As long as SnSexTe1-x remains in the cubic crystal structure, it is predicted to be a TCI. We show systematic decrease of the bulk carrier density with the increasing Se concentration, demonstrating that the alloying principle works. In addition, we map out the phase diagram of the cubic to the orthorhombic structural transition as a function of the Se concentration. This was made possible by studying alloy nanoplates which remain single-crystalline and is either in the cubic or the orthorhombic phase, in contrast to bulk alloys that would exhibit polycrystalline grains. Lastly, we investigate systematically the ferroelectric transition associated with the structural transition from the cubic to the rhombohedral phase for SnSexTe1-x. This is the first ferroelectric transition study of the alloy system SnSexTe1-x.