  The two-dimensional Hubbard model exhibits superconductivity with d-wave
symmetry even at half-filling in the presence of next-nearest neighbor hopping.
Using plaquette cluster dynamical mean-field theory with a continuous-time
quantum Monte Carlo impurity solver, we reveal the non-Fermi liquid character
of the metallic phase in proximity to the superconducting state. Specifically,
the low-frequency scattering rate for momenta near (\pi, 0) varies
non-monotonously at low temperatures, and the dc conductivity is T-linear at
elevated temperatures with an upturn upon cooling. Evidence is provided that
pairing fluctuations dominate the normal-conducting state even considerably
above the superconducting transition temperature.
