Competing phases in epitaxial vanadium dioxide at nanoscale

Yogesh Sharma,Ilia N Ivanov,Xiang Gao,Martin V Holt,Liam Collins,Zhaoliang Liao,Ho Nyung Lee,Gyula Eres,Elizabeth Skoropata,Changhee Sohn,Thomas Z Ward,Nina Balke,Nouamane Laanait,Sergei V Kalinin

doi:10.1063/1.5115784

Yogesh Sharma, Ilia N Ivanov + Show 12 more

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https://doi.org/10.1063/1.5115784

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Phase competition in correlated oxides offers tantalizing opportunities as many intriguing physical phenomena occur near the phase transitions. Owing to a sharp metal-insulator transition (MIT) near room temperature, the correlated vanadium dioxide (VO2) exhibits a strong competition between insulating and metallic phases, which is important for practical applications. However, the phase boundary undergoes a strong modification when strain is involved, yielding complex phase transitions. Here, we report the emergence of nanoscale M2 phase domains in VO2 epitaxial films under anisotropic strain relaxation. The competing phases of the films are imaged by multilength-scale probes, detecting the structural and electrical properties in individual local domains. Competing evolution of the M1 and M2 phases indicates the critical role of lattice-strain on both the stability of the M2 Mott phase and the energetics of the MIT in VO2 films. This study demonstrates how strain engineering can be utilized to design phase states, which allow deliberate control of MIT behavior at the nanoscale in epitaxial VO2 films.

Highlights

The M2 phase is believed to have comparable free energy to M1 in bulk VO2, which can be stabilized by modulating strain
The metastability of the M2 phase highlights its importance as a Mott insulator, which could potentially settle the debate about the coupled nature of Peierls and Mott-Hubbard mechanisms responsible for the metal-insulator transition (MIT) in VO2.48,49 Combined local imaging of structural and electronic properties of the M2 phase across the transition are lacking
Using multimodal imaging techniques, including large area probes averaging over multiple phase domains of different character, we directly image the coexistence of distinct metallic and insulating nanoscale phase domains across the MIT

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Introduction

To gain insight into the local electronic properties, we employed temperature dependent conducting atomic force microscopy (c-AFM) to study the nanoscale phase evolution in VO2 films with strain. Such domains of different electronic states were previously observed in strain relaxed VO2/TiO2 (001) films using infrared (IR) nanoimaging techniques.12,29,30,53 in contrast to previous reports in which the observations were limited to the qualitative information from the IR scattering amplitude and phase images, our results provide details on the electronic phase evolution by measuring the current of a single localized domain at nanoscale (see the supplementary material).

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