Calendar of Events
Superconductivity in ultra-quantum matter : optimizing Tc
Speaker: André-Marie Tremblay (Département de physique and RQMP Université de Sherbrooke)
Title: Superconductivity in ultra-quantum matter : optimizing Tc
Superconductors based on CuO2 conducting layers (cuprates) are still model systems for future generations of materials that could be superconducting at ambient pressure and temperature. They are appealing on a fundamental level because they are strongly quantum-fluctuating compounds with spin one-half carriers, interaction strength that is comparable to kinetic energy and a single band crossing the Fermi level.
However, the single band crossing the Fermi level has both copper and oxygen orbital content. Since the interactions are mostly on the copper orbitals, the one-band Hubbard model, where the oxygen orbital content is neglected, has been very successful in explaining many of the observed properties. In this talk, it is shown that the oxygen orbital is a useful witness that gives insights into the mechanism of superconductivity in cuprates when it is taken into account.
Using cluster generalizations of dynamical mean-field theory  we explain three apparently unrelated experiments that suggest how to optimize Tc in cuprates:
i) NMR experiments that show that Tc is optimized by maximizing oxygen hole content 
ii) Scanning Tunneling spectroscopy that shows that Tc is optimized by decreasing the charge transfer gap  and
iii) Neutron experiments that show that Tc is optimized by increasing superexchange .
The unified explanation of these three experiments that is offered  also explains the mechanism for superconductivity in cuprates. The results suggest new avenues to discover compounds that superconduct at even higher temperature .
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Host: Kristjan Haule