【报告题目】：Adiabatic-impulse approximation and first-order quantum phase transition in non-Hermitian systems
【报告人】：童先奇，北京师范大学
【报告时间】：1月22日10:00-12:00
【报告地点】：29-414
【报告摘要】：This study explores adiabatic dynamic transitions in non-Hermitian systems and discovers a novel quantum phase transition in a two-dimensional model.
First, in the non-Hermitian Landau-Zener models, we investigate the dynamical transition both in parity-time symmetric and symmetry-broken regimes. Considering the complex nature of the energy of the non-Hermitian systems, the absolute value of the gap was used to determine the relaxation rate of the system. To show the dynamics of the phase transitions, the relative population is used to estimate the topological defect density in nonequilibrium phase transitions, rather than the excitations in the corresponding Hermitian systems. The result shows that the adiabatic-impulse approximation, which is fundamental to the Kibble-Zurek mechanism, may be adapted to the parity-time symmetric non-Hermitian Landau-Zener models to examine the dynamics near the critical point.
Secondly, the non-Hermitian extension of quasicrystals provides a highly tunable system for exploring novel material phases. While extended-localized phase transitions have been observed in one dimension, quantum phase transitions in higher dimensions and various system sizes remain unexplored. Here, we show the discovery of a new critical phase and first-order quantum phase transition induced by imaginary domains in the two-dimensional Haldane model with a quasicrystal potential on the upper boundary. Initially, we illustrate a phase diagram that evolves with the amplitude and phase of the quasiperiodic potential, which is divided into three distinct phases by two critical boundaries: phase (I) with extended wave functions, PT-restore phase (II) with localized wave functions, and a critical phase (III) with multifunctional wave functions. To characterize the wavefunctions in these distinct phases, we introduce a low-energy approximation theory and an effective two
【邀请人】：高先龙教授
