Graduate School in Nonlinear Science

Sponsored by The Danish Research Agency

MIDIT                              OFD                          CATS
Modelling, Nonlinear Dynamics      Optics and Fluid Dynamics    Chaos and Turbulence Studies
and Irreversible Thermodynamics    Risø National Laboratory     Niels Bohr Institute and 
Technical University of Denmark    Building 128                 Department of Chemistry
Building 321                       P.O. Box 49                  University of Copenhagen 
DK-2800 Lyngby                     DK-4000 Roskilde             DK-2100 Copenhagen Ø
Denmark                            Denmark                      Denmark


Verner K. Thorsmolle
Los Alamos National Laboratory,
S K 763, Los Alamos, NM 87545

Wednesday, September 12, 2001, 14:00 h
at IMM, Bldg. 305, Room 018, DTU

Abstract: The c-axis Josephson Plasma Resonance (JPR) in highly anisotropic layered cuprate superconductors originates from the interlayer tunneling of Cooper pairs. The JPR frequency is determined by the interlayer Josephson current, ?pē=J0 , and where < cos ? > is the interlayer phase coherence factor. In the presence of a magnetic field this phase difference is altered by the misalignment of pancake vortices along the c-axis, which causes the suppression of the critical current density and the JPR frequency. The JPR frequency thus probes the correlations of pancake vortices along the c-axis and is an excellent tool with which to probe the various phases of the magnetic vortex phase diagram in high-Tc superconductors.

We are presenting the first measurements of the JPR in high-Tc superconductor as a function of temperature and magnetic field employing THz-TDS in transmission and directly measured in the time-domain. Using this technique we find evidence for a linelike structure of the liquid phase in Tl-2212 above the calculated melting transition. YBCO with anisotropy ~8 has a liquid phase of vortex lines, while Bi-2212 with anisotropy ~600 has a liquid phase of pancake vortices. The anisotropy is defined as \u03B3=?c/?ab (c-axis penetration depth over ab-plane penetration depth). It is a surprising result that Tl-2212 behaves as YBCO in this respect despite the closer anisotropy (~150) to Bi-2212.