Versatile Tunability of the Metal Insulator Transition in (TiO2)m/(VO2)m Superlattices

Gyula Eres,Changhee Sohn,Shinbuhm Lee,Milan Radovic,Xingye Lu,Gerd Duscher,Jong Mok Ok,Alessandro R Mazza,Thorsten Schmitt,Chenze Liu,John Nichols,Daniel E Mcnally,Ho Nyung Lee

doi:10.1002/adfm.202004914

Abstract

AbstractIn contrast to perovskites that share only common corners of cation‐occupied octahedra, binary‐oxides in addition share edges and faces increasing the versatility for tuning the properties and functionality of reduced dimensionality systems of strongly correlated oxides. This approach for tuning the electronic structure is based on the ability of X‐ray spectroscopy methods to monitor the creation and transformation of occupied and unoccupied electronic states produced by interface coupling and lattice distortions. X‐ray diffraction reveals a new range of structural metastability in (TiO2)m/(VO2)m/TiO2(001) superlattices with m = 1, 3, 5, 20, 40, and electrical transport measurements show metal insulator transition (MIT) behavior typically associated with presence of high oxygen vacancy concentrations. However, X‐ray absorption spectroscopy (XAS) at the Ti and V L3,2‐edge and resonant inelastic X‐ray scattering (RIXS) at the Ti and V L3‐edge show no excitations characteristic of oxygen vacancy induced valance change in V and negligible intensities in Ti RIXS. The unexpected absence of oxygen vacancy related states in the X‐ray spectroscopy data suggests that superlattice fabrication is capable of suppressing oxygen vacancy formation while still affording a wide tunability range of the MIT. Achieving a wide range of MIT tunability while reducing or eliminating oxygen vacancies that are detrimental to electrical properties is highly desirable for technological applications of strongly correlated oxides.

Highlights

The approach for interpretation of the metal insulator transition (MIT) includes two different starting points.[10]
The dimerization of Vanadium dioxide (VO2) is an archetypal strongly correlated the V atoms is believed to indicate that the MIT is driven by material that exhibits a metal insulator transition (MIT) con- structural distortions and strong electron-lattice coupling that comitant with a structural phase transition (SPT) slightly are the features of Peierls physics.[11]
The reason binary oxides are more versatile models for exploring strong correlation effects is that in contrast to perovskites that only share common corners of cation-occupied octahedra, binary-oxides can in addition share common edges and faces facilitating direct cation-to-cation interactions

Summary

Introduction

The approach for interpretation of the MIT includes two different starting points.[10]. The starting point for understanding the complex landscape of coupling between the structural and the electronic degrees of freedom driving the MIT is the qualitative picture, provided by the molecular orbital (MO) model proposed by Goodenough.[11] This model uses the orbital configuration and the orbital populations of the V 3d energy levels to interpret the electronic structure changes during the VO2 MIT. The X-ray spectroscopy data demonstrate that fabrication of superlattices is a highly versatile method for exploring novel properties and functionalities in reduced dimensionality systems of strongly correlated oxides in general

Results and Discussion

Characterization of the Electronic Structure of TiO2 using XAS and RIXS

Characterization of the Electronic Structure of VO2 using XAS and RIXS

Conclusions

Experimental Section

Conflict of Interest