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Physics and Astronomy

Physics & Astronomy Colloquium

3:30 PM, Friday, September 12, 2008
Room 155, Chem-Phys Building

Dr. Vidya Madhavan
Department of Physics
Boston College

Unsolved Mysteries of High Temperature Superconductivity: Clues to the Pairing Mechanism
After two decades of intense research on high-temperature superconductors, there is no consensus on the basic question: what is the mechanism that causes electron pairing? The high Tc problem remains one of the most important outstanding problems in condensed matter physics today. Even as we explore the possibility that pairing in these unconventional superconductors proceeds without the involvement of a bosonic glue, we have recently made exciting progress in identifying candidates that could potentially mediate pairing. In this talk, I will discuss our recent STM investigations of the electron-doped cuprate superconductor Pr0.88 LaCe0.12 CuO4 (PLCCO with Tc = 24 K). Our spectra reveal superconducting gaps with coherence peaks that disappear above Tc. In addition, multiple step/peak-like features are observed outside the gap. Such features in STM spectra are suggestive of bosonic excitations that couple strongly to the electrons. Analysis of the data indicates that the observed (bosonic) mode energy in PLCCO lies at 10.52.5 meV which is much lower than the bosonic mode observed in hole-doped BSCCO. The energy scale of our mode is the same as the magnetic resonance mode (spin-excitations) in PLCCO measured by inelastic neutron scattering but is also consistent with a low energy acoustic mode. Finally, I will show STM data that indicates an electronic origin rather than phonons and discuss the implications of this data for the pairing mechanism.

Refreshments will be served in CP 155 at 3:15 PM