Large phase relaxation length in the topological surface states of epitaxial Bi2-xSnxTe3 thin films

TL;DR

This study demonstrates a record-high phase relaxation length of approximately 250 nm in the topological surface states of epitaxial Bi2-xSnxTe3 thin films, advancing the understanding of surface state transport in topological insulators.

Contribution

It reports the suppression of bulk conduction and the measurement of an exceptionally large phase relaxation length in topological surface states of Bi2-xSnxTe3 thin films.

Findings

Large phase relaxation length (~250 nm) at 1.8 K.

Non-monotonic temperature dependence of magnetoresistance ratio.

Suppressed bulk conduction enabling surface state characterization.

Abstract

A topological insulator (TI), a new quantum state featured with the topologically-protected surface state (TSS) originating from its peculiar topology in band structure, has attracted much interest due to academic and practical importance. Nonetheless, a large contribution of the bulk conduction, induced by unintended doping by defects, has hindered the characterization of the unique surface state and the utilization of it into a device. To resolve this problem, we have investigated the transport properties of epitaxial Bi2-xSnxTe3 thin films with varying x. With the bulk conduction being strongly suppressed, the TSS is separately characterized, resulting in a large phase relaxation length of ~250 nm at 1.8 K, a record-high value in TIs. In addition, the magnetoresistance ratio (MR) has shown a non-monotonic temperature dependence with a maximum value at an elevated temperature depending on x. These results are associated with the compensation of carriers and, we believe, provide an important step for the application of topological insulators for developing novel functional devices based on the topological surface states.