Epitaxial thin films of pyrochlore iridate Bi_{2+x}Ir_{2-y}O_{7-delta}: structure, defects and transport properties

TL;DR

This study reports the successful epitaxial growth and detailed characterization of Bi2Ir2O7 pyrochlore iridate thin films, revealing their structural, defect, and complex transport properties relevant for topological phenomena.

Contribution

It demonstrates a method for growing high-quality pyrochlore iridate thin films and provides insights into their defect structures and transport behaviors, advancing experimental exploration of topological properties.

Findings

Films have larger lattice constants than bulk crystals.

Presence of Bi_Ir antisite defects and oxygen deficiency.

Transport shows multiple charge carriers and spin-orbit effects.

Abstract

While pyrochlore iridate thin films are theoretically predicted to possess a variety of emergent topological properties, experimental verification of these predictions can be obstructed by the challenge in thin film growth. Here we report on the pulsed laser deposition and characterization of thin films of a representative pyrochlore compound Bi2Ir2O7. The films were epitaxially grown on yttria-stabilized zirconia substrates and have lattice constants that are a few percent larger than that of the bulk single crystals. The film composition shows a strong dependence on the oxygen partial pressure. Density-functional-theory calculations indicate the existence of Bi_Ir antisite defects, qualitatively consistent with the high Bi: Ir ratio found in the films. Both Ir and Bi have oxidation states that are lower than their nominal values, suggesting the existence of oxygen deficiency. The iridate thin films show a variety of intriguing transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on temperature, antilocalization corrections to conductance due to spin-orbit interactions, and linear positive magnetoresistance.