BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:New Effects in Vortex Resistivity and Pinning in Optimally Doped Y
 Ba2Cu3O6+x - Ben Morgan\, University of Cambridge
DTSTART:20060215T111500Z
DTEND:20060215T121500Z
UID:TALK4664@talks.cam.ac.uk
CONTACT:cb203
DESCRIPTION:Using an innovative microwave technique developed in the QM gr
 oup\, precise measurements of the flux-flow resistivity rho_ff(T) and the 
 pinning force alpha_p(T) have been made on high-purity samples of optimall
 y doped YBa2Cu3O6+x (TC = 93.5 K) in the mixed state\, at temperatures dow
 n to 1 K. Several new effects have been observed\, despite the subject bei
 ng the most intensely studied of cuprate superconductors. The effective re
 sistivity of the vortex cores is found to exhibit the same metalinsulator 
 transition as has been reported in the DC resistivity of lower-TC cuprates
 \, with rho_ff(T) growing logarithmically at low temperatures. The pinning
  force acting upon the vortices has been found to increase exponentially w
 ith temperature below 30 K\, consistent with published critical-current me
 asurements but difficult to explain using the popular theory of thermally 
 activated flux creep. At temperatures just below TC\, a sharp peak in alph
 a_p(T) has been seen\, whose form is strikingly similar to that of the int
 rinsic peak effect reported for the low-TC superconductor NbSe2. Finally\,
  the magnetic field dependence of the London penetration depth has been in
 ferred from the apparent field dependences of rho_ff and alpha_p at low te
 mperatures\, the results being consistent with published mu-SR measurement
 s.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
END:VEVENT
END:VCALENDAR