Epitaxial thin films of pyrochlore iridate Bi2+xIr2-yO7-\u03b4: structure, defects and transport properties

W C Yang,Y Losovyj,K Park,W K Zhu,Q X Jia,M Starr,H M Liu,A P Chen,S X Zhang,J J Heremans,J A Acosta,Z Li,N Li,Y T Xie,C G Tao

doi:10.1038/s41598-017-06785-w

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 BiIr 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.

Highlights

Iridates have recently emerged as a fertile ground for novel topological electronic states that arise from the interplay of electron interactions and spin-orbit coupling[1,2,3,4,5,6,7,8,9]
Thin films were grown by pulsed laser deposition (PLD) using two targets that were prepared via a solid state reaction method with IrO2 and Bi2O3 as source materials at Ir/Bi ratios of 1 and 3
X-ray diffraction (XRD) measurements suggest that thin films are epitaxially grown on the yttrium-stabilized zirconia (YSZ) substrates along the [111] direction of a cubic phase

Summary

Introduction

Iridates have recently emerged as a fertile ground for novel topological electronic states that arise from the interplay of electron interactions and spin-orbit coupling[1,2,3,4,5,6,7,8,9]. Theoretical studies on pyrocholore iridate thin films have suggested a variety of emergent topological properties, including the quantized anomalous Hall conductance[44] and the correlated Chern insulator[45] that are otherwise not accessible in bulk samples. While these topological properties have yet been realized experimentally, remarkable transport phenomena have been observed in thin films, including a linear magnetoresistance (MR) up to 35 Tesla in Bi-22739 and a cooling field-dependent, assymetric MR in Eu-22740. Thin films show a broad spectrum of electronic transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on T, antilocalization, and linear positive magnetoresistance

Methods

Results

Conclusion