The gestalt of strongly correlated superconductivity
by
JC Séamus Davis(Brookhaven Nat. Lab. / Cornell University/ St. Andrews University)
→
Europe/Stockholm
Oskar Klein Auditorium
Oskar Klein Auditorium
Description
We review the challenge of finding a unified mechanism for Cooper pairing in correlated superconductors e.g. copper-‐oxides, iron-‐arsenides and heavy fermions. Our experimental context is the comparison of electronic structure imaging using spectroscopic imaging STM results for each of these systems. Because this technique can determine simultaneously the k-‐space structure of the superconductivity and the r-‐space structure of proximate broken symmetry states, it provides some of the best indications of the gestalt of strongly correlated superconductivity.
In copper-‐oxides there are two well-‐known broken-‐symmetry states: the Q≠0 density waves (Science 315, 1380 (2007)) and Q=0 intra-‐unit-‐cell nematic (Nature
466, 374 (2010)) that can be visualized directly. Real-‐space imaging of these two states shows that they are closely linked (Science 333, 426 (2012). The concurrent k-‐space imaging is achieved by using Fourier-‐transform STM and reveals the evolution of the Fermi arcs with doping (Nature 454, 1072 (2008)). Now we report that both these broken-‐symmetry states disappear at a critical doping, where that the k-‐space topology also undergoes an abrupt transition from arcs to closed contours. Similarly motivated SI-‐STM studies of iron-‐arsenides discovered the electronic nematicity of the parent state (Science 327, 181 (2010)), while k-‐space imaging revealed anisotropy, magnitude, and relative orientations of the energy gaps of the superconducting state (Science 336, 563 (2010)), and combined imaging shows a strong interplay of these two phenomena at the nanoscale (Nature Physics
9, 220 (2013)). Finally, corresponding SI-‐STM studies allowed the first imaging of heavy fermions (Nature 465, 570 (2010)), which presaged the first visualization of k-‐space structure of superconducting energy, gaps in a heavy fermion system (Nature Physics 9, 468 (2013)).
But could these very disparate observations possibly be related within a unified mechanism? A simple synthesis is possible: The strong, on-‐site, repulsive electron-‐ electron interactions that are the proximate cause of such superconductivity are more typically drivers of commensurate magnetism; suppression of commensurate antiferromagnetism (AF) usually allows unconventional superconductivity to emerge; it is between these AF and SC phases that the ’intertwined’ electronic ordered phases (density waves, nematic etc.) are usually discovered. We discuss a logical basis, motivated by this analysis, for a unified explanation of the relationship between the antiferromagnetic electron-‐electron interactions, the intertwined ordered phases and the correlated superconductivity in all these systems.
