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TT: Tiefe Temperaturen

TT 27: Symposium Twenty Years High-T_c Cuprates - Recent Progress

TT 27.1: Hauptvortrag

Donnerstag, 30. März 2006, 09:30–10:00, HSZ 02

Vorticity in the phase diagram of cuprates: evidence from Nernst effect and torque magnetometry — •N. P. Ong — Department of Physics, Princeton University, Princeton, New Jersey 08544, U.S.A.

A key question in cuprates is whether the critical transition at T_c corresponds to the BCS gap-closing scenario or the loss of long-range phase coherence. The observation in LSCO of a large Nernst signal that extends from above the T_c “dome” to a temperature T_onset with a peak value of 130 K has provided strong evidence for the phase-disordering scenario¹. The vortex-Nernst signal implies that the pair condensate remains finite above T_c. Similar evidence for a large vortex Nernst signal has been reported in the hole-doped cuprates Bi 2201, Bi 2212, Bi 2223, YBCO, but not in the electron-doped cuprate NdCeCuO. The existence of vorticity in turn implies that significant 2D diamagnetism must exist above T_c. Recently, the diamagnetic signal has been confirmed using torque magnetometry. The signal remains robust in fields up to 45 T and scales closely with the vortex-Nernst signal over a broad range of T. I will review the evidence and discuss implications for the phase diagram and the pseudogap state.
1. Yayu Wang, Lu Li and N. P. Ong, cond-mat/0510470.