Insights from newer theoretical approaches
It is possible to design models with fermions that do not have a sign problem. It opens the way to large system studies that give results for these models that are close to exact. This kind of approach has allowed us to understand that, in a theory where antiferromagnetic hot spots are present, upon increasing the coupling constant, there is a maximum attainable superconducting Tc. The existence of such a maximum Tc as a function of a parameter seems to be quite general. It is seen in the attractive Hubbard model for example. Also, the validity of the Eliashberg approach, that neglects vertex corrections, has been tested within such a fermion-sign free model.
Cluster dynamical mean-field calculations seem to reproduce much of the phenomenology of both cuprates and layered BEDT organics. They suggest qualitative differences between strongly correlated superconductivity and superconductivity that results from pairing through long-wavelength fluctuations.
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