Topological Anderson insulator in two-dimensional non-Hermitian systems

We study the disorder-induced phase transition in two-dimensional non-Hermitian systems.First,the applicability of the noncommutative geometric method(NGM)in non-Hermitian systems is examined.By calculating the Chern number of two different systems(a square sample and a cylindrical one),the numerical results calculated by NGM are compared with the analytical one,and the phase boundary obtained by NGM is found to be in good agreement with the theoretical prediction.Then,we use NGM to investigate the evolution of the Chern number in non-Hermitian samples with the disorder effect.For the square sample,the stability of the non-Hermitian Chern insulator under disorder is confirmed.Significantly,we obtain a nontrivial topological phase induced by disorder.This phase is understood as the topological Anderson insulator in non-Hermitian systems.Finally,the disordered phase transition in the cylindrical sample is also investigated.The clean non-Hermitian cylindrical sample has three phases,and such samples show more phase transitions by varying the disorder strength:(1)the normal insulator phase to the gapless phase,(2)the normal insulator phase to the topological Anderson insulator phase,and(3)the gapless phase to the topological Anderson insulator phase.

Observation of an acoustic non-Hermitian topological Anderson insulator

The interaction of band topology and disorder can give rise to intriguing phenomena.One paradigmatic example is the topological Anderson insulator,whose nontrivial topology is induced in a trivial system by disorders.In this study,we investigate the efect of purely non-Hermitian disorders on topological systems using a one-dimensional acoustic lattice with coupled resonators.Specifically,we construct a theoretical framework to describe the non-Hermitian topological Anderson insulator phase solely driven by disordered loss modulation.Then,the complete evolution of non-Hermitian disorder-induced topological phase transitions,from an initial trivial phase to a topological Anderson phase and finally to a trivial Anderson phase,is revealed experimentally using both bulk and edge spectra.Interestingly,topological modes induced by non-Hermitian disorders to be immune to both weak Hermitian and non-Hermitian disorders.These findings pave the way for future research on disordered non-Hermitian systems for novel wave manipulation.

Topological and dynamical phase transitions in the Su–Schrieffer–Heeger model with quasiperiodic and long-range hoppings

Disorders and long-range hoppings can induce exotic phenomena in condensed matter and artificial systems.We study the topological and dynamical properties of the quasiperiodic SuSchrier-Heeger model with long-range hoppings.It is found that the interplay of quasiperiodic disorder and long-range hopping can induce topological Anderson insulator phases with nonzero winding numbers ω=1,2,and the phase boundaries can be consistently revealed by the divergence of zero-energy mode localization length.We also investigate the nonequilibrium dynamics by ramping the long-range hopping along two different paths.The critical exponents extracted from the dynamical behavior agree with the Kibble-Zurek mechanic prediction for the path with W=0.90.In particular,the dynamical exponent of the path crossing the multicritical point is numerical obtained as 1/6~0.167,which agrees with the unconventional finding in the previously studied XY spin model.Besides,we discuss the anomalous and non-universal scaling of the defect density dynamics of topological edge states in this disordered system under open boundary condictions.