How Bad Metals Turn Good: Spectroscopic Signatures of Resilient Quasiparticles

We investigate transport in strongly correlated metals. Within dynamical mean-field theory, we calculate the resistivity, thermopower, optical conductivity and thermodynamic properties of a hole-doped Mott insulator. Two well-separated temperature scales are identified: T(FL) below which Landau Fermi liquid behavior applies, and T(MIR) above which the resistivity exceeds the Mott-Ioffe-Regel value and bad-metal behavior is found. We show that quasiparticle excitations remain well defined above T(FL) and dominate transport throughout the intermediate regime T(FL) </~ T </~ T(MIR). The lifetime of these resilient quasiparticles is longer for electronlike excitations and this pronounced particle-hole asymmetry has important consequences for the thermopower. The crossover into the bad-metal regime corresponds to the disappearance of these excitations and has clear signatures in optical spectroscopy.