Crossovers and critical scaling in the one-dimensional transverse-field Ising model

TL;DR

This paper investigates the thermodynamic scaling behavior of the one-dimensional transverse-field Ising model near its quantum critical point, revealing unique features in the Grüneisen ratio and entropy accumulation that aid experimental identification.

Contribution

It provides a detailed analysis of the critical scaling and crossover behavior of thermodynamic quantities in the model, including the unusual constant Grüneisen ratio at the critical field.

Findings

The Grüneisen ratio diverges as a power law when approaching the QCP at zero temperature.

At the critical field, the Grüneisen ratio approaches a constant upon decreasing temperature.

Entropy is maximized near the QCP despite the unusual scaling behavior.

Abstract

We consider the scaling behavior of thermodynamic quantities in the one-dimensional transverse-field Ising model near its quantum critical point (QCP). Our study has been motivated by the question about the thermodynamical signatures of this paradigmatic quantum critical system and, more generally, by the issue of how quantum criticality accumulates entropy. We find that the crossovers in the phase diagram of temperature and (the non-thermal control parameter) transverse field obey a general scaling ansatz, and so does the critical scaling behavior of the specific heat and magnetic expansion coefficient. Furthermore, the Gr\"{u}neisen ratio diverges in a power-law way when the QCP is accessed as a function of the transverse field at zero temperature, which follows the prediction of quantum critical scaling. However, at the critical field, upon decreasing the temperature, the Gr\"uneisen ratio approaches a constant instead of showing the expected divergence. We are able to understand this unusual result in terms of a peculiar form of the quantum critical scaling function for the free energy; the contribution to the Gr\"uneisen ratio vanishes at the linear order in a suitable Taylor expansion of the scaling function. In spite of this special form of the scaling function, we show that the entropy is still maximized near the QCP, as expected from the general scaling argument. Our results establish the telltale thermodynamic signature of a transverse-field Ising chain, and will thus facilitate the experimental identification of this model quantum-critical system in real materials.