Condensed Matter Physics Seminar

J. C. Seamus Davis, Cornell University & Brookhaven National Laboratory

Friday 10 May 2013, 1100-1200
C1 Physics Building

Title: Spectroscopic Imaging STM Studies of Unconventional Superconductivity

Abstract: Spectroscopic imaging STM is a technique for mapping simultaneously the real-space (r-space) and momentum-space (k-space) electronic structure of electronic matter. We review its application in searches for the mechanism of unconventional superconductivity in copper-oxides, iron-arsenides, and heavy fermions.

In copper-oxides, we showed that the mysterious pseudogap is associated with electronic symmetry breaking (Science 315, 1380 (2007); Science 333, 426 (2011)). Our concurrent momentum-space imaging was achieved by using Fourier-transform STM (Nature 454, 1072 (2008)). Now we report the relationship between the r-space symmetry breaking and k-space Fermi Arc, and how they evolve through the enigmatic quantum critical point of hole-doped cuprates.

In iron-arsenides, we discovered and first visualized (Science 327, 181 (2010)) the now famous nematic phase whose suppression generates the superconductivity. Next, we explored the predictions that, if electron-electron interactions mediate the Cooper pairing, then specific and distinct momentum-anisotropic superconducting energy gaps should exist on the different electronic bands. Here we discovered the anisotropy, magnitude, and relative orientations of the energy gaps on multiple bands (Science 336, 563 (2010)) as predicted.

In heavy fermion materials, we carried out the first direct observation of heavy fermion formation - splitting of a light k-space band into two new heavy fermion bands due to the hybridization process (Nature 465, 570 (2010)). Most recently ( we achieved the first visualization of the Cooper pairing mechanism of any heavy-fermion superconductor (CeCoIn5).