Excitations of the bimodal Ising spin glass on the brickwork lattice

TL;DR

This paper uses an exact algorithm to study low-energy excitations in the bimodal Ising spin glass on the brickwork lattice, revealing finite degeneracy of the first excited state and a universal energy gap of 2J, contrasting with square lattice behavior.

Contribution

It provides the first detailed analysis of excitation degeneracies and energy gaps for the bimodal Ising spin glass on the brickwork lattice, highlighting differences from the square lattice case.

Findings

Degeneracy of first excited state per ground state is finite in the thermodynamic limit.

Energy gap is 2J, consistent across finite and infinite systems.

Low-temperature specific heat dominated by a T^{-2} exponential term.

Abstract

An exact algorithm is used to investigate the distributions of the degeneracies of low-energy excited states for the bimodal Ising spin glass on the brickwork lattice. Since the distributions are extreme and do not self-average, we base our conclusions on the most likely values of the degeneracies. Our main result is that the degeneracy of the first excited state per ground state and per spin is finite in the thermodynamic limit. This is very different from the same model on a square lattice where a divergence proportional to the linear lattice size is expected. The energy gap for the brickwork lattice is obviously 2J on finite systems and predicted to be the same in the thermodynamic limit. Our results suggest that a 2J gap is universal for planar bimodal Ising spin glasses. The distribution of the second contribution to the internal energy has a mode close to zero and we predict that the low-temperature specific heat is dominated by the leading term proportional to $T^{-2} \exp(-2J/kT)$.