paper

Longitudinal-field fidelity susceptibility analysis of the - transverse-field Ising model around

arXiv:2601.01893 · doi:10.1016/j.physa.2025.131245

Abstract

The square-lattice - transverse-field (TF) Ising model was investigated with the exact diagonalization (ED) method. In order to analyze the TF-driven phase transition, we applied the longitudinal-field fidelity susceptibility , which is readily evaluated via the ED scheme. Here, the longitudinal field couples with the absolute value of the magnetic moment rather than the raw so that the remedied fidelity susceptibility exhibits a peak around the critical point; note that the spontaneous magnetization does not appear for the finite-size systems. As a preliminary survey, the modified fidelity susceptibility is applied to the analysis of criticality for , where a number of preceding results are available. Thereby, properly scaling the distance from the multi-criticality, , the data were cast into the crossover-scaling formula, and the multi-critical exponent for is estimated. The result is cross-checked by the numerically evaluated -function behavior.

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