Abstract
The prototypical metal-insulator transition in VO2 at 340 K is from a high-temperature rutile phase to a low-temperature monoclinic phase. The lower symmetry of the monoclinic structure removes the degeneracy of the two equivalent directions of the tetragonal structure, giving rise to twin domains. Since formation of domain walls require energy most needle-like monoclinic single crystal are single-domain. The mixed metal-insulator state in self-heated needle-like single crystals exhibits various domain patterns, the most remarkable being static insulating triangular domains embedded in the metal and narrow insulating domains sliding along the metallic background in the direction of the electric current. Reported here are results obtained for some rare needle-like twinned VO2 single crystals. Such sample revealed a unique feature: joint static triangular twins emit sliding twin domains, first overlapping and later disjoining. Dark and bright twins and dim metallic background were seen for optimal orientation under a microscope, due to polarization by reflection.
Highlights
The prototypical metal-insulator transition in VO2 at 340 K is from a high-temperature rutile phase to a low-temperature monoclinic phase
Domain patterns of twins in the lower symmetry phase are visible under the optical microscope in reflected polarized light from surfaces of VO2 in the low- temperature, monoclinic phase[1]
The same result may be obtained via polarization by reflection; this requires finding the optimal orientation of the sample with respect to the incident light, for maximal contrast between the two types of domains
Summary
The prototypical metal-insulator transition in VO2 at 340 K is from a high-temperature rutile phase to a low-temperature monoclinic phase. I-M domain patterns in the mixed state of VO2 crystals are visible under the microscope due to the much higher reflectivity of the insulating phase relative to that of the metal.
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