Quantum interference in macroscopic crystals of non-metallic Bi$_2$Se$_3$

TL;DR

This study reveals a novel quantum interference effect involving spin in non-metallic Bi$_2$Se$_3$ crystals, with unusually large amplitude signals indicating long phase coherence lengths and potential topological surface state contributions.

Contribution

It demonstrates the existence of a new magnetofingerprint signal in non-metallic Bi$_2$Se$_3$ crystals, highlighting long phase coherence and the role of topological states in conductance.

Findings

Observed magnetofingerprint signals 200-500 times larger than universal conductance fluctuations.

Identified long phase breaking lengths in non-metallic Bi$_2$Se$_3$ crystals.

Linked in-gap conducting states to topological surface states.

Abstract

Photoemission experiments have shown that Bi$_2$Se$_3$ is a topological insulator. By controlled doping, we have obtained crystals of Bi$_2$Se$_3$ with non-metallic conduction. At low temperatures, we uncover a novel type of magnetofingerprint signal which involves the spin degrees of freedom. Given the mm-sized crystals, the observed amplitude is 200-500$\times$ larger than expected from universal conductance fluctuations. The results point to very long phase breaking lengths in an unusual conductance channel in these non-metallic samples. We discuss the nature of the in-gap conducting states and their relation to the topological surface states.