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Symmetry and localization in periodic crystals: triviality of Bloch bundles with a fermionic time-reversal symmetry

TitleSymmetry and localization in periodic crystals: triviality of Bloch bundles with a fermionic time-reversal symmetry
Publication TypeJournal Article
Year of Publication2015
AuthorsMonaco, D, Panati, G
JournalActa Applicandae Mathematicae, vol. 137, Issue 1, 2015, pages: 185-203
Abstract

We describe some applications of group- and bundle-theoretic methods in solid state physics, showing how symmetries lead to a proof of the localization of electrons in gapped crystalline solids, as e.g. insulators and semiconductors.
We shortly review the Bloch-Floquet decomposition of periodic operators, and the related concepts of Bloch frames and composite Wannier functions. We show that the latter are almost-exponentially localized if and only if there exists a smooth periodic Bloch frame, and that the obstruction to the latter condition is the triviality of a Hermitian vector bundle, called the Bloch bundle. The rôle of additional Z_2-symmetries, as time-reversal and space-reflection symmetry, is discussed, showing how time-reversal symmetry implies the triviality of the Bloch bundle, both in the bosonic and in the fermionic case. Moreover, the same Z_2-symmetry allows to define a finer notion of isomorphism and, consequently, to define new topological invariants, which agree with the indices introduced by Fu, Kane and Mele in the context of topological insulators.

URLhttp://urania.sissa.it/xmlui/handle/1963/34468
DOI10.1007/s10440-014-9995-8

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