Symmetry, Exceptional Points, and Phase Transitions

Symmetry, Exceptional Points, and Phase Transitions - Featured

Title: Symmetry, Exceptional Points, and Phase Transitions
When: Thursday, March 21, 2024, 12:00
Place: Department of Theoretical Condensed Matter Physics, Faculty of Sciences, Module 5, Seminar Room (5th Floor)
Speaker: Ipsita Mandal, Shiv Nadar Institute of Eminence and Freiburg Institute for Advanced Studies, Germany.

I will focus on non-Hermitian (NH) “Hamiltonians”, which appear in the effective description of various physical settings, ranging from classical photonics to dissipative quantum materials. Using simple examples, I will discuss some topological aspects of such systems, related to the concept of Exceptional Points (EPs). EPs showcase degeneracies at which two or more eigenvalues and eigenvectors coalesce. Second-order EPs are by far the most studied due to their abundance, requiring only the tuning of two real parameters. Higher-order EPs generically require more fine-tuning, and are thus assumed to play a much less prominent role. However, I will show that physically relevant symmetries make higher-order EPs dramatically more abundant and conceptually richer. I will discuss the emergence of unexpected odd-order EPs in the presence of sublattice symmetries , which exhibit enhanced sensitivity in the behaviour of the eigenvector collapse in their neighbourhood, depending on the path chosen to approach the singular point. Finally, I will discuss the non-Hermitian skin effect, which has no Hermitian counterpart.

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