Optical properties ofV1−xCrxO2compounds under high pressure

Abstract

Raman and infrared transmission and reflectivity measurements were carried out at room temperature and high pressure ͑0-15 GPa͒ on V 1−x Cr x O 2 compounds. Raman spectra were collected at ambient conditions on the x = 0.007 and 0.025 materials, which are characterized by different insulating monoclinic phases ͑M3 and M2, respectively͒, while infrared spectra were collected on the x = 0.025 sample only. The present data were compared with companion results on undoped VO 2 ͓E. Arcangeletti et al., Phys. Rev. Lett. 98, 196406 ͑2007͔͒, which is found at ambient conditions in a different, third insulating monoclinic phase, named M1. This comparison allowed us to investigate the effects of different extents of structural distortions ͑Peierls distortion͒ on the lattice dynamics and the electronic properties of this family of compounds. The pressure dependence of the Raman spectrum of VO 2 and Cr-doped samples shows that all the systems retain the monoclinic structure up to the highest explored pressure, regardless the specific monoclinic structure ͑M1, M2, and M3͒ at ambient condition. Moreover, the Raman spectra of the two Cr-doped samples, which exhibit an anomalous behavior over the low-pressure range ͑P Ͻ 8 GPa͒, merge into that of VO 2 in the high-pressure regime and are all found into a common monoclinic phase ͑a possible fourth kind phase͒. Combining Raman and infrared results on both the VO 2 and the present data, we found that a common metallic monoclinic phase appears accessible in the high-pressure regime at room temperature for both undoped and Cr-doped samples independently of the different extents of Peierls distortion at ambient conditions. This finding differs from the behavior observed at ambient pressure, where the metallic phase is found only in conjunction with the rutile structure. The whole of these results suggests a major role of the electron correlations, rather than of the Peierls distortion, in driving the metal-insulator transition in vanadium dioxide systems, thus opening to new experimental and theoretical queries.

Inhomogeneity of the ultrafast insulator-to-metal transition dynamics of VO2

“…For microcrystals in the M1 phase, o V À O B620 cm À 1 , and the amount of doping or impurity is o 1% (ref. 44). …”

Direct Observation of Nanoscale Peltier and Joule Effects at Metal–Insulator Domain Walls in Vanadium Dioxide Nanobeams

“…10,25,26 Thermal images of the NB taken at 355 K under an applied 10 μA sinusoidal current are presented in Figure 2. As discussed, periodic domains are indicative of homogeneous substrate adhesion and are clearly observed in the optical image depicted in Figure 2a,b (greyscale image); this domain configuration remained stationary for the duration of the thermoreflectance measurement.…”

Modification of electronic structure in compressively strained vanadium dioxide films

“…Thus, for experimental measurements of these systems to provide meaningful insight, the external parameters, the intrinsic interacting degrees of freedom, and the resulting properties must all be well characterized. Hence, measurements on samples subject to external perturbations, for example pressure and strain [5][6][7][8][9][10] , can provide additional insight into the underlying physics of these systems.…”