Stability conditions for fermionic Ising spin-glass models in the presence of a transverse field

TL;DR

This paper investigates the stability of the spin-glass phase in a fermionic Ising model under a transverse magnetic field, revealing multiple instabilities and the limitations of traditional stability criteria near quantum critical points.

Contribution

It introduces a detailed analysis of the stability conditions using replica methods in a quantum fermionic spin-glass model, highlighting new instability mechanisms beyond the replicon.

Findings

Replicon instability is always present in the RS solution.

Eigenvalues λ± indicate additional instabilities that increase with the transverse field.

Instabilities are prominent near the first order transition boundary.

Abstract

The stability of spin-glass (SG) phase is analyzed in detail for a fermionic Ising SG (FISG) model in the presence of a magnetic transverse field $\Gamma$. The fermionic path integral formalism, replica method and static approach have been used to obtain the thermodynamic potential within one step replica symmetry breaking ansatz. The replica symmetry (RS) results show that the SG phase is always unstable against the replicon. Moreover, the two other eigenvalues $\lambda_{\pm}$ of the Hessian matrix (related to the diagonal elements of the replica matrix) can indicate an additional instability to the SG phase, which enhances when $\Gamma$ is increased. Therefore, this result suggests that the study of the replicon can not be enough to guarantee the RS stability in the present quantum FISG model, especially near the quantum critical point. In particular, the FISG model allows changing the occupation number of sites, so one can get a first order transition when the chemical potential exceeds a certain value. In this region, the replicon and the $\lambda_{\pm}$ indicate instability problems for the SG solution close to all range of first order boundary.