Wednesday, August 3, 2016

Organics and other unconventional superconductors

Organics  and other unconventional superconductors
Layered organic superconductors are primarily half-filled and, as a function of temperature and pressure, exhibit a Mott transition, as well as antiferromagnetic, superconducting and spin-liquid phases. They are thus interesting compounds to gain insights into hole-doped cuprates as well. The latest experimental results, presented at this workshop, suggest that a half-filled spin-liquid compound has the same spin dynamics as a doped version of that compound, despite the fact that one is an insulator and another one a conductor. From the point of view of theory, RVB and CDMFT phase diagrams share similarities.

Superconductiviy in the Mott insulating organics is certainly unusual, but another unusual type of superconductivity was discussed. Isotopic oxygen-enrichment (or Nb doping) of strontium titanate has revealed a paraelectric quantum critical point surrounded by a dome of superconductivity. Although electron-phonon interactions can possibly explain superconductivity in this case, calculations would need to be done in the highly unusual anti-adiabatic regime where the Fermi energy is smaller than the Debye frequency of the optical phonons apparently involved here. 

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