Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La(2-x)Sr(x)CuO(4)

Abstract

By using new and previous measurements of the $ab$-plane conductivity $σ_1^{ab} (ω,T)$ of La$_{2-x}$Sr$_x$CuO$_{4}$ (LSCO) it is shown that the spectral weight $W = \int_0^Ω{σ_1^{ab} (ω,T) dω}$ obeys the same law $W = W_0 - B(Ω) T^2$ which holds for a conventional metal like gold, for $Ω$'s below the plasma frequency. However $B(Ω)$, which measures the "thermal response" of the charge system, in LSCO exhibits a peculiar behavior which points towards correlation effects. In terms of hopping models, $B(Ω)$ is directly related to an energy scale $t_T$, smaller by one order of magnitude than the full bandwidth $t_0 \sim W_0$.