q-Gaussian Crossover in Overlap Spectra toward 3D Edwards-Anderson Criticality

We introduce a spectral approach to characterizing the three-dimensional Edwards-Anderson spin glass. By analyzing the eigenvalue statistics of overlap matrices constructed from two-dimensional cross sections, we identify a crossover from the Wigner semicircle law at high temperatures toward a Gaussian distribution, which is consistently attained near the spin-glass critical point. Visible for different distributions of the random coupling, the Gaussian distribution can potentially serve as a robust spectral indicator of criticality. Remarkably, the spectral density is well described by Tsallis statistics, with the entropic index q evolving from q=-1 (semicircle, T=∞) to q=1 (Gaussian) at T_{c}, revealing a statistical structure inside the paramagnetic phase. We find q≤1 within numerical precision. While the local level statistics remain consistent with Gaussian orthogonal ensemble statistics, reflecting standard level repulsion, the temperature dependence appears mainly in the global spectral density. Our results present spectral statistics as a computationally efficient complement to multireplica correlator methods and provide a new perspective on cooperative and critical phenomena in disordered systems.