| We study the half-filled two-dimensional Hubbard model with a focus on the moderate coupling regime below the critical Coulomb repulsion strength for the Mott metal-insulator transition. Using plaquette cluster dynamical mean-field theory and solving the impurity problem by continuous-time quantum Monte Carlo simulations, we find a sequence of phases at low but finite temperature upon an increase in the interaction strength for a non-zero next-nearest neighbor hopping: (i) a metal at very weak coupling, (ii) a superconducting state with d-wave order parameter symmetry at moderate coupling, (iii) a metal with non-Fermi liquid properties, and (iv) a Mott insulator at strong coupling. The superconducting state emerges upon cooling from a non-Fermi liquid with unusual transport properties. |
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