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Center for Nonlinear Studies |
The origin of non-BCS superconductivity in strongly correlated electron systems poses a long standing open problem in modern condensed matter physics. Traditionally, this phenomenon is exhibited by the high-Tc cuprates. However, according to recent proposals, it can also be observed in experiments with ultracold atomic gases. Theoretically it has been realized long ago that microscopic lattice inhomogeneities, on the nanoscale, can stabilize the superconducting order in purely repulsive systems. However, this superconductivity turns out to be quite fragile at sufficiently strong electron repulsion.
In the present work we discuss the mechanism of a non-BCS nature which can stabilize a superconducting state in a strongly repulsive electron system. Our analysis is based on a frustrated 2D Hubbard model with spatially modulated electron hoppings. We demonstrate how kinetic energy frustration can lead to the robust d-wave superconductivity at arbitrarily large on-site repulsion. Observation of this phenomenon requires fine tuning of the parameters in the model and, therefore, high level of control in experiments. We believe that this is achievable in cold atom systems, e.g. using 40K in specially crafted optical lattices.