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Condensed Matter Seminars

ics Condensed Matter
Thursday, September 15, 2016
11:00 AM
Physics Building, Room 313
Mumtaz Qazilbash [Host: Utpal Chatterjee]
William and Mary
"Exploring metal-insulator transitions with optical microscopy and spectroscopy"

The study of metal-insulator, structural and magnetic phase transitions in materials with strongly interacting electrons is a challenging frontier of condensed matter physics. The challenge is to disentangle the contributions of charge, lattice, spin and orbital degrees of freedom to phase transitions. I will report on the optical properties of two materials that undergo thermally-induced metal-insulator transitions accompanied by structural and/or magnetic instabilities: vanadium dioxide (VO2) and the manganite La0.67Sr0.33MnO3. Infrared micro-spectroscopy and micro-ellipsometry measurements on crystals of VO2 reveal that its insulating phases are Mott-Hubbard insulators, not Peierls insulators. Scanning near-field infrared microscopy (SNIM) allows us to directly image nano-scale metallic puddles that appear at the onset of the first-order metal-insulator transition (MIT) in VO2 films. We find that the patterns of metallic domains are reproducible upon repeated thermal cycles across the MIT and point to the important role of imperfections in films.  In contrast to VO2, recent SNIM data shows time dependence of near-field infrared amplitude in a La0.67Sr0.33MnO3 film which we attribute to fluctuating conductivity in the vicinity of its second order metal-insulator transition.

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