The specific heat of the rwo-dimensional +/-J Ising model

TL;DR

This study investigates the specific heat behavior of the two-dimensional $\

Contribution

It introduces a new perspective on the specific heat of the 2D $\

Findings

The specific heat can be negative in certain regions, indicating frustration.

The specific heat does not diverge on part of the phase boundary, contradicting previous findings.

The negative specific heat region includes the Nishimori line and a significant part of the phase diagram.

Abstract

The specific heat of the two-dimensional $\pm J$ Ising model has been investigated by the numerical transfer matrix method and Monte Carlo simulations from a new point of view. The region where a part of the specific heat takes the negative value has been investigated, which is characteristic of frustrated systems and reflects the non-trivial degeneracy of the ground state. The region mentioned above is found to be fairly large in the $p-T$ plane ($p$ is the concentration of the ferromagnetic bond and $T$ is the temperature). Moreover, it includes the Nishimori line. Namely, it includes a part of the paramagnetic-ferromagnetic phase boundary, on which the specific heat cannot diverge. The present result indicates that the specific heat does not diverge at least on a part of the paramagnetic-ferromagnetic phase boundary above the multicritical point, which is in conflict with previous results.