Phase transitions in the tetramerized Su–Schrieffer–Heeger chain differentiated by disordered non-Hermitian imaginary potentials

Abstract

In this work, phase transitions of the non-Hermitian tetramerized Su–Schrieffer–Heeger (TSSH) chain are investigated by periodically introducing the non-Hermitian on-site imaginary potentials U1=(iγ1,iγ2,−iγ1,−iγ2) or U2=(iγ1,−iγ2,−iγ1,iγ2), with γ1 and γ2 being the imaginary-potential strengths. Numerical results show that these imaginary potentials induce the topologically nontrivial transitions of the topological properties of the TSSH chain in different ways. Namely, U1 only modifies the two-fold degenerated topologically nontrivial region, without affecting the other topological phases. By contrast, U2 can reduce the topologically trivial region and modify the four-fold degenerated topologically nontrivial region by introducing the new topological phase transition. Moreover, when the imaginary potentials are influenced by the Anderson disorder, the bulk states display obvious localization. Disordered U2 leads to the widening of the topologically nontrivial regions. Based on these results, we believe this work provides insights into the influences of on-site imaginary potentials on the topological properties of non-Hermitian TSSH structures.