Specific heat of thermally driven chains

TL;DR

This paper studies the nonequilibrium specific heat of a driven harmonic oscillator chain coupled to heat baths, revealing how temperature-dependent system-bath interactions influence heat capacity in steady energy flux conditions.

Contribution

It provides the first explicit calculation of specific heat in a spatially extended, driven nonequilibrium system with local interactions.

Findings

Existence of a well-defined thermodynamic limit for long chains.

Specific heat depends on the friction coefficients of system-bath couplings.

Temperature dependence of specific heat arises from temperature-dependent bath couplings.

Abstract

We investigate the thermal responses of a harmonic oscillator chain coupled at its boundaries to heat baths held at different temperatures. This setup sustains a steady energy flux, continuously dissipating heat into both reservoirs. By introducing slow variations in the bath temperatures, we quantify the resulting excess heat currents and thereby obtain the nonequilibrium heat capacity matrix at fixed but arbitrary temperature differences. We demonstrate the existence of a well-defined thermodynamic limit for long chains. The specific heat associated with energy exchanges with a single bath depends on the difference in friction coefficients governing the system-bath couplings. That thermokinetic effect is typical for nonequilibrium response. When the couplings with the thermal baths acquire temperature dependence, the specific heat correspondingly inherits a nontrivial temperature dependence, in sharp contrast with equilibrium. Our results provide the first explicit determination of specific heat(s) in a locally interacting, spatially extended driven system. Beyond its exact solvability, the model may offer a natural nonequilibrium extension of the Dulong-Petit law, capturing the high-temperature behavior of driven molecules.