Imaging the nanoscale phase separation in vanadium dioxide thin films at terahertz frequencies

H. T. Stinson, A. Sternbach, O. Najera, R. Jing, A. S. Mcleod, T. V. Slusar, A. Mueller, L. Anderegg, H. T. Kim, M. Rozenberg, D. N. Basov

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Vanadium dioxide (VO2) 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 VO2 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 VO2, which account for a continuous temperature dependence of the optical response of the VO2 in the insulating state.

Original languageEnglish (US)
Article number3604
JournalNature communications
Issue number1
StatePublished - Dec 1 2018
Externally publishedYes

Bibliographical note

Funding Information:
We acknowledge the valuable discussions about optical design and principles of operation for customized terahertz instruments with Dr. Ian Gregory of TeraView Limited, Cambridge. Research at ETRI is supported by a principal project (18ZB1320). Work at UC-San Diego and Columbia University is supported by ARO-W911nf-17-1-0543. D.N. B. is the Gordon and Betty Moore Foundation’s EPiQS Initiative investigator, Grant GBMF4533. The development of THz nano-imaging is supported by ONR-DURIP: N00014-18-1-2737. The development of the cryogenic scanner and rapid sample exchange is supported by DE-SC-0012375 and DE-SC0018218. M.R. acknowledges the support by public grants from the French National Research Agency (ANR), project LACUNES No. ANR-13-BS04-0006-01, and the French–US Associated International Laboratory on Nanoelectronics funded by CNRS.

Publisher Copyright:
© 2018, The Author(s).


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