Direct observation of the M2 phase with its Mott transition in a VO2 film

In VO2, the explicit origin of theinsulator-to-metal transition is still disputable between Peierls and Mottinsulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerizedvanadium ions. However, the origin of the M2 phase is still obscure. Here, we study a granular VO2 film using conductive atomic force microscopy andRaman scattering. Upon the structuraltransition from monoclinic to rutile, we observe directly an intermediate state showing the coexistence of monoclinic M1 and M2 phases. The conductivity near thegrain boundary in this regime is six times larger than that of the grain core, producing a donut-like landscape. Our results reveal an intra-grainpercolation process, indicating that VO2 with the M2 phase is a Mottinsulator.

Source: Applied Physics Letters - December 6, 2016 Category: Physics Authors: Hoon Kim, Tetiana V. Slusar, Dirk Wulferding, Ilkyu Yang, Jin-Cheol Cho, Minkyung Lee, Hee Cheul Choi, Yoon Hee Jeong, Hyun-Tak Kim and Jeehoon Kim Source Type: research