Thermoelectric effects in a strongly correlated model for Na$_x$CoO$_2$

TL;DR

This paper investigates thermoelectric properties of a strongly correlated t-J model on a frustrated triangular lattice, validating high-frequency approximations and exploring the impact of hopping parameter sign on thermopower.

Contribution

It applies exact diagonalization to compute dynamical thermal response functions in a frustrated lattice model, confirming the validity of high-frequency formalism for thermoelectric properties.

Findings

Dynamical thermal response functions are weakly frequency-dependent.

High-frequency formalism accurately predicts thermopower and Lorenz number.

Sign change of hopping parameter affects thermopower enhancement.

Abstract

Thermal response functions of strongly correlated electron systems are of appreciable interest to the larger scientific community both theoretically and technologically. Here we focus on the infinitely correlated t-J model on a geometrically frustrated two-dimensional triangular lattice. Using exact diagonalization on a finite sized system we calculate the dynamical thermal response functions in order to determine the thermopower, Lorenz number, and dimensionless figure of merit. The dynamical thermal response functions is compared to the infinite frequency limit and shown to be very weak functions of frequency, hence, establishing the validity of the high frequency formalism recently proposed by Shastry for the thermopower, Lorenz number, and the dimensionless figure of merit. Further, the thermopower is demonstrated to have a low to mid temperature enhancement when the sign of the hopping parameter $t$ is switched from positive to negative for the geometrically frustrated lattice considered.