Direct observation of the M2 phase with its Mott transition in a VO${}_2$ film

Abstract

In VO${}_2$, the explicit origin of the insulator-to-metal transition is still disputable between Peierls and Mott insulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerized vanadium ions. However, the origin of the M2 phase is still obscure. Here, we study a granular VO${}_2$ film using conductive atomic force microscopy and Raman scattering. Upon the structural transition from monoclinic to rutile, we observe directly an intermediate state showing the coexistence of monoclinic M1 and M2 phases. The conductivity near the grain boundary in this regime is six times larger than that of the grain core, producing a donut-like landscape. Our results reveal an intra-grain percolation process, indicating that VO${}_2$ with the M2 phase is a Mott insulator.

References in corpus (4)

• Mott transition in VO2 revealed by infrared spectroscopy and nano-imaging
• Evidence for a Structurally-driven Insulator-to-metal Transition in VO2: a View from the Ultrafast Timescale
• Direct Observation of Decoupled Structural and Electronic Transitions and an Ambient Pressure Monoclinic-Like Metallic Phase of VO${}_2$
• Large epitaxial bi-axial strain induces a Mott-like phase transition in VO2