Mott Variable Range Hopping and Weak Antilocalization Effect in Heteroepitaxial Na2IrO3 Thin Films

TL;DR

This study reports on heteroepitaxial Na2IrO3 thin films exhibiting variable range hopping conductivity and weak antilocalization effects, supporting their potential as topological insulators with surface states.

Contribution

It demonstrates high-quality heteroepitaxial Na2IrO3 films with detailed electronic and optical characterization, revealing topological insulator features.

Findings

Resistivity follows 3D variable range hopping from 300 K to 40 K.

Optical gap of about 200 meV observed.

Weak antilocalization effect detected below 3 T and 25 K.

Abstract

Iridate thin films are a prerequisite for any application utilizing their cooperative effects resulting from the interplay of stron spin-orbit coupling and electronic correlations. Here, heteroepitaxial Na2IrO3 thin films with excellent (001) out-of-plane crystalline orientation and well defined in-plane epitaxial relationship are presented on various oxide substrates. Resistivity is dominated by a three-dimensional variable range hopping mechanism in a large temperature range between 300 K and 40 K. Optical experiments show the onset of a small optical gap of about 200 meV and a splitting of the Ir 5d-t2g manifold. Positive magnetoresistance below 3 T and 25 K shows signatures of a weak antilocalization effect. This effect can be associated with surface states in a topological insulator and hence supports proposals for a topological insulator phase present in Na2IrO3.