Condensed Matter Physics Seminar

What lies above: evidence for a vortex liquid state above Tc in the cuprates

Professor N. P. Ong
Princeton University
Tuesday, April 26, 2005
Higgins 235, 1pm

The nature of the pseudogap state that lies above the superconducting "dome" defined by Tc in the phase diagram of cuprates has been the focus of much research. About 4 years ago, Nernst effect experiments began to show evidence for vortex excitations above Tc in hole-doped cuprates. The evidence implies that, in the cuprates, Tc reflects the collapse of long-range phase coherence rather than vanishing of the pair condensate. In the past year, the magnetization has been measured in fields up to 32 Tesla using torque magnetometry. The results confirm this scenario. What lies above the Tc line is a phase-disordered vortex liquid masquerading as the "normal" state. Surprisingly, the high-temperature dissipative vortex liquid lacks a linear-response regime even in a 10-Oe field.