Bad-metallic behavior of doped Mott insulators

Employing Nernst-Einstein decomposition sigma = e(2)chi D-c of the conductivity s onto charge susceptibility (compressibility) chi(c) and diffusion constant D, we argue that the bad-metallic behavior of sigma in the regime of high temperatures and lightly doped insulator is dominated by the strong temperature and doping dependence of chi(c). In particular, we show how at small dopings chi(c) strongly decreases towards undoped-insulating values with increasing temperature and discuss a simple picture leading to the linear-in-temperature resistivity with the prefactor increasing inversely with decreasing concentration (p) of doped holes, rho proportional to T/p. On the other hand, D shows weak temperature and doping dependence in the corresponding regime. We support our arguments by numerical results on the two-dimensional Hubbard model and discuss the proposed picture from the experimental point of view.