29 March 2022 Tue 4 pm

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Non-Hermitian systems such as open or lossy systems are ubiquitous in na- ture. The basic ways to create a non-Hermitian system are by employing the on-site gain and loss energies or imbalance/non-reciprocal hoppings. This leads to the directional asymmetry in the system and some critical points known as exceptional points with special properties. In this talk, I will discuss the multipartite non-Hermitian Su-Schrieffer-Heeger model as a pro- totypical example of one-dimensional systems with several sublattice sites for unveiling intriguing insulating and metallic phases with no Hermitian coun- terparts. These phases are characterized by composite cyclic loops of multiple complex-energy bands encircling single or multiple exceptional points (EPs) on the parametric space of real and imaginary energy. We show the topology of these composite loops can be quantified by a nonadiabatic cyclic geometric phase which includes contributions only from the participating bands. We analytically derive a complete phase diagram with the phase boundaries of the model. We further examine the connection between encircling of multiple EPs by complex-energy bands on parametric space and associated topology.

References

[1]  Ritu Nehra and Dibyendu Roy. Topology of multipartite non-hermitian one- dimensional systems, 2022. arXiv:2201.12297.
[2]  Zongping Gong, Yuto Ashida, Kohei Kawabata, Kazuaki Takasan, Sho Hi- gashikawa, and Masahito Ueda. Topological Phases of Non-Hermitian Sys- tems. Phys. Rev. X, 8:031079, Sep 2018.
[3]  Baogang Zhu, Rong Lu ̈, and Shu Chen. PT symmetry in the non-Hermitian Su-Schrieffer-Heeger model with complex boundary potentials. Phys. Rev. A, 89:062102, Jun 2014.
[4]  Shi-Dong Liang and Guang-Yao Huang. Topological invariance and global Berry phase in non-Hermitian systems. Phys. Rev. A, 87:012118, Jan 2013.

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