# The internal energy, the magnetization and the specific heat of the Heisenberg XX chain at low temperatures

## TL;DR

This paper derives low-temperature power series expansions for the magnetization, internal energy, and specific heat of the Heisenberg XX chain, revealing how magnetic field strength influences their behavior through different power laws.

## Contribution

It provides novel low-temperature series expansions for key thermodynamic quantities of the Heisenberg XX chain, highlighting the impact of magnetic field strength on their behavior.

## Key findings

- Series coefficients depend logarithmically on fugacity.
- Different power laws emerge depending on the magnetic field relative to the critical point.
- The effects of spin coupling and magnetic field vary across the critical point.

## Abstract

We derive power series expansions for the magnetization, the internal energy, and the specific heat of the Heisenberg XX chain that are valid at low temperatures. The coefficients of the series obtained depend logarithmically on the fugacity. It is shown that depending on whether the magnetic field exceeds or not the critical point, the effects of either the coupling of the spins and the magnetic field can have different characters, as indicated by the different power laws established.