Universality classes of Anderson localization transitions in disordered three-dimensional non-Hermitian systems with exceptional points

We conduct a numerical study of wave localization in disordered three-dimensional non-Hermitian systems featuring exceptional points. The energy spectrum of a disordered non-Hermitian Hamiltonian, exhibiting both parity-time and parity-particle-hole symmetries, forms a cross in the complex energy plane, with an exceptional point fixed at the origin. Near the exceptional point, the system undergoes a disorder-driven quantum phase transition from extended to localized states, which is characterized as an Anderson localization transition in non-Hermitian systems. Notably, we identify a universal critical exponent that remains independent of the distribution of random variables. The model also supports Anderson localization transitions away from the exceptional points, albeit with different critical exponents. Furthermore, we investigate wave localization in a non-Hermitian system lacking parity-time symmetry, revealing distinct universality classes. By comparing the obtained critical exponents with those reported in the literature, we conclude that the presence of exceptional points introduces new universality classes that extend beyond the established 38-fold symmetry classification for non-Hermitian systems.