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

TL;DR

This study investigates the frequency-dependent thermal response of the charge system in La(2-x)Sr(x)CuO(4), revealing correlation effects and a smaller energy scale for thermal response compared to the full bandwidth.

Contribution

It demonstrates that the spectral weight follows a T^2 law similar to metals but exhibits a peculiar frequency-dependent behavior indicating strong correlation effects.

Findings

Spectral weight obeys W = W_0 - B(Ω) T^2 law below plasma frequency.

B(Ω) shows peculiar behavior indicating correlation effects.

Thermal response energy scale t_T is an order of magnitude smaller than the bandwidth.

Abstract

By using new and previous measurements of the $ab$-plane conductivity $\sigma_1^{ab} (\omega,T)$ of La$_{2-x}$Sr$_x$CuO$_{4}$ (LSCO) it is shown that the spectral weight $W = \int_0^\Omega {\sigma_1^{ab} (\omega,T) d\omega}$ obeys the same law $W = W_0 - B(\Omega) T^2$ which holds for a conventional metal like gold, for $\Omega$'s below the plasma frequency. However $B(\Omega)$, 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, $B(\Omega)$ is directly related to an energy scale $t_T$, smaller by one order of magnitude than the full bandwidth $t_0 \sim W_0$.