Topological triple phase transition in non-Hermitian quasicrystals with complex asymmetric hopping

The triple phase transitions or simultaneous transitions of three different phases, namely topological, parity-time (PT) symmetry breaking, and metal-insulator transitions, are observed in an extension of PT symmetric non-Hermitian Aubry-Andr\'e-Harper model. In this model, besides non-Hermitian complex quasi-periodic onsite potential, non-Hermiticity is also included in the nearest-neighbor hopping terms. Moreover, the nearest-neighbor hopping terms is also quasi-periodic. The presence of two non-Hermitian parameters, one from the onsite potential and another one from the hopping part, ensures PT symmetry transition in the system. In addition, tuning these two non-Hermitian parameters, we identify a parameters regime, where we observe the triple phase transition. Following some recent studies, an electrical circuit based experimental realization of this model is also discussed.