Universal Charge and Spin Response in Optimally Doped Antiferromagnets

TL;DR

This paper numerically investigates charge and spin responses in the $t-J$ model at finite temperatures, revealing temperature-independent local spin correlations and optical conductivity behaviors relevant to cuprates.

Contribution

It demonstrates universal charge and spin response behaviors in the $t-J$ model at intermediate doping, connecting them to entropy effects in cuprates.

Findings

Local spin correlation function is temperature-independent.

Optical conductivity follows a universal form involving hyperbolic tangent.

Charge and spin responses are anomalous and linked to large entropy.

Abstract

Charge and spin response in the planar $t-J$ model at finite temperatures are investigated numerically, in the regime corresponding to cuprates at intermediate doping. We show that the local spin correlation function is $T$-independent, leading to $\chi''(\omega<J) \propto \tanh (\omega/2 T)$. The current correlation function $C(\omega)$ appears to be $T$- as well as $\omega$-independent, and the optical conductivity $\sigma \propto (1- e^{-\omega/T})/\omega$. Such anomalous response functions are brought in connection with the large entropy persisting at $T<J$.