Seminar

Visualizing Two Gaps in the High-TC Superconductor (Bi-Pb)2Sr2CuO6+δ

Michael C. Boyer
MIT
Tuesday, February 19, 2008
Higgins 235, 2:30 pm

The relationship between the superconducting and pseudogap states in high temperature superconductors is of much debate.  Is the pseudogap state made up of preformed Cooper pairs which gain phase coherence as temperature is lowered through TC resulting in superconductivity?  Or, is the pseudogap a separate, competing state which can coexist with superconductivity?  I will present results from our scanning tunneling microscopy study of (Bi-Pb)2Sr2CuO6+δ which follows a single, atomically resolved region from below to above TC.  We find a large, inhomogeneous gap which exists below TC and continues to exist virtually unchanged through and above TC.  We also find a small, homogeneous gap below TC which is temperature dependent and vanishes at TC.  Due to the differing temperature dependence we identify the small and large gaps as the superconducting gap and pseudogap respectively.  Both of these gaps, and hence states, simultaneously coexist at the same spatial location below TC indicating that the pseudogap is not purely a precursor state to the superconducting state.  Finally, I will present our recent study which follows impurity resonances through TC.  We find the impurity resonances preserved above TC indicating that they interact with the pseudogap.  The nature of their interaction provides further insight into the pseudogap state itself.