Imaging the nanoscale phase separation in vanadium dioxide thin films at terahertz frequencies.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 30190517.
- Also identified by DOI 10.1038/s41467-018-05998-5 and PMC identifier 6127259.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Vanadium dioxide (VO<sub>2</sub>) is a material that undergoes an insulator-metal transition upon heating above 340 K. It remains debated as to whether this electronic transition is driven by a corresponding structural transition or by strong electron-electron correlations. Here, we use apertureless scattering near-field optical microscopy to compare nanoscale images of the transition in VO<sub>2</sub> thin films acquired at both mid-infrared and terahertz frequencies, using a home-built terahertz near-field microscope. We observe a much more gradual transition when THz frequencies are utilized as a probe, in contrast to the assumptions of a classical first-order phase transition. We discuss these results in light of dynamical mean-field theory calculations of the dimer Hubbard model recently applied to VO<sub>2</sub>, which account for a continuous temperature dependence of the optical response of the VO<sub>2</sub> in the insulating state.