Observation of three-dimensional Dirac semimetal state in topological insulator Bi2Se3

TL;DR

This paper provides the first experimental evidence of a three-dimensional Dirac semimetal state in the topological insulator Bi2Se3, identified through magneto-transport measurements and analysis of quantum oscillations.

Contribution

It demonstrates the existence of a 3D Dirac semimetal state in Bi2Se3 and links it to strain and spin-orbit coupling effects, advancing understanding of topological phase transitions.

Findings

Observation of Shubnikov-de Haas oscillations indicating 3D Dirac semimetal state

Detection of a non-trivial pi Berry phase from quantum oscillation analysis

Correlation of the semimetal state with strain and selenium vacancies

Abstract

The three dimensional (3D) topological insulators are predicted to exhibit a 3D Dirac semimetal state in critical regime of topological to trivial phase transition. Here we demonstrate the first experimental evidence of 3D Dirac semimetal state in topological insulator Bi2Se3 with bulk carrier concentration of ~ 10^19 cm^{-3}, using magneto-transport measurements. At low temperatures, the resistivity of our Bi2Se3 crystal exhibits clear Shubnikov-de Haas (SdH) oscillations above 6T. The analysis of these oscillations through Lifshitz-Onsanger and Lifshitz-Kosevich theory reveals a non-trivial pi Berry phase coming from 3D bands, which is a decisive signature of 3D Dirac semimetal state. The large value of Dingle temperature and natural selenium vacancies in our crystal suggest that the observed 3D Dirac semimetal state is an outcome of enhanced strain field and weaker effective spin-orbit coupling.