Wednesday, September 7, 2011, 11:00 am — Bldg. 480 conference room
Superconductor-insulator transition was studied in ultrathin
YBa2Cu3O7-x films by electrostatic charging using an ionic liquid
as dielectric. A clear transition between superconducting and
insulating behavior was realized and finite size scaling analysis
suggests the presence of a quantum critical point. In the presence
of magnetic field, a cleaner superconductor-insulator transition
was realized and proved to be a quantum phase transition. Further
depletion of holes caused electrons to be accumulated in the film
and the superconductivity to be recovered on the electron doped
side. By changing the polarity of the gate voltage, an underdoped
sample was tuned into the overdoped regime. Transport measurements
showed a series of anomalous features compared to chemically doped
bulk samples and an unexpected two-step mechanism for
electrostatic doping was revealed. These anomalous behaviors
suggest that there is an electronic phase transition in the Fermi
surface around the optimal doping level.
Hosted by: Ivan Bozovic
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