BEGIN:VCALENDAR VERSION:2.0 PRODID:Data::ICal 0.22 BEGIN:VEVENT DESCRIPTION:Mumtaz Qazilbash\, William and Mary\n\n
The study of metal-in
sulator\, structural and magnetic phase transitions in materials with stro
ngly interacting electrons is a challenging frontier of condensed matter p
hysics. The challenge is to disentangle the contributions of charge\, latt
ice\, spin and orbital degrees of freedom to phase transitions. I will rep
ort on the optical properties of two materials that undergo thermally-indu
ced 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 crystal
s of VO2 reveal that its insulating phases are Mott-Hubbard insulators\, n
ot Peierls insulators. Scanning near-field infrared microscopy (SNIM) allo
ws us to directly image nano-scale metallic puddles that appear at the ons
et of the first-order metal-insulator transition (MIT) in VO2 films. We fi
nd that the patterns of metallic domains are reproducible upon repeated th
ermal cycles across the MIT and point to the important role of imperfectio
ns in films.  \;In contrast to VO2\, recent SNIM data shows time depen
dence 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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