University of Minnesota
School of Physics & Astronomy

Condensed Matter Sack Lunch Seminar

Tuesday, January 27th 2009
12:20 pm:
Speaker: Prof. Vidya Madhavan, Boston College
Subject: New Developments in Scanning Tunneling Microscopy of High Temperature Superconductors
The speaker is a candidate for the Cond. Matter Experimentalist Asst. Prof. position.

The 'high-Tc problem' remains one of the most important outstanding problems in condensed matter physics today. After two decades of intense research there is no consensus on the basic question: what is the mechanism that responsible for pairing? 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 Pr0.88LaCe0.12CuO4-δ (PLCCO) (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 reveals bosonic modes at 10.5±2.5 meV and 3 meV which are much lower in energy than the bosonic mode observed in hole-doped Bi2212. These energy scales match the magnetic resonance modes (spin-excitations) in PLCCO measured by inelastic neutron scattering. I will show that both the local mode energy and the intensity are correlated with the local gap energy scale and discuss the implications of our observations on the pairing issue. I will also briefly discuss recent atomic resolution images and spectroscopy on the parent compound of a pnictide superconductor SrFe2As2. I will compare our data with contradictory LEED on identical samples and explore the possible reasons for this puzzling contradiction.

The weekly calendar is also available via subscription to the physics-announce mailing list, and by RSS feed.