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Symmetry-protected nodal phases in non-Hermitian systems
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.ORCID-id: 0000-0002-9739-2930
2019 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 4, artikel-id 041406Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Non-Hermitian (NH) Hamiltonians have become an important asset for the effective description of various physical systems that are subject to dissipation. Motivated by recent experimental progress on realizing the NH counterparts of gapless phases such as Weyl semimetals, here we investigate how NH symmetries affect the occurrence of exceptional points (EPs), that generalize the notion of nodal points in the spectrum beyond the Hermitian realm. Remarkably, we find that the dimension of the manifold of EPs is generically increased by one as compared to the case without symmetry. This leads to nodal surfaces formed by EPs that are stable as long as a protecting symmetry is preserved, and that are connected by open Fermi volumes. We illustrate our findings with analytically solvable two-band lattice models in one and two spatial dimensions, and show how they are readily generalized to generic NH crystalline systems.

Ort, förlag, år, upplaga, sidor
2019. Vol. 99, nr 4, artikel-id 041406
Nyckelord [en]
Quantum optics, Dirac semimetal
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
teoretisk fysik
Identifikatorer
URN: urn:nbn:se:su:diva-166133DOI: 10.1103/PhysRevB.99.041406ISI: 000456809000002OAI: oai:DiVA.org:su-166133DiVA, id: diva2:1289079
Forskningsfinansiär
VetenskapsrådetKnut och Alice Wallenbergs StiftelseTillgänglig från: 2019-02-15 Skapad: 2019-02-15 Senast uppdaterad: 2019-12-12Bibliografiskt granskad
Ingår i avhandling
1. Solvable Topological Boundaries
Öppna denna publikation i ny flik eller fönster >>Solvable Topological Boundaries
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The hallmark of topological phases of matter is the presence of robust boundary states. In this dissertation, a formalism is developed with which analytical solutions for these states can be straightforwardly obtained by making use of destructive interference, which is naturally present in a large family of lattice models. The validity of the solutions is independent of tight-binding parameters, and as such these lattices can be seen as a subset of solvable systems in the landscape of tight-binding models. The approach allows for a full control of the topological phase of the system as well as the dispersion and localization of the boundary states, which makes it possible to design lattice models possessing the desired topological phase from the bottom up. Further applications of this formalism can be found in the fields of higher-order topological phases—where boundary states localize to boundaries with a codimension larger than one—and of non-Hermitian Hamiltonians—which is a fruitful approach to describe dissipation, and feature many exotic features, such as the possible breakdown of bulk-boundary correspondence—where the access to exact solutions has led to new insights.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Physics, Stockholm University, 2019. s. 91
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
teoretisk fysik
Identifikatorer
urn:nbn:se:su:diva-166135 (URN)978-91-7797-630-1 (ISBN)978-91-7797-631-8 (ISBN)
Disputation
2019-04-12, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Anmärkning

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 7: Submitted. Paper 8: Manuscript.

Tillgänglig från: 2019-03-20 Skapad: 2019-02-22 Senast uppdaterad: 2019-12-12Bibliografiskt granskad

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Carlström, JohanKunst, Flore K.Bergholtz, Emil J.
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