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arxiv: 1708.07420 · v4 · pith:4X4PNIPFnew · submitted 2017-08-24 · ❄️ cond-mat.mes-hall

Topological invariants for Floquet-Bloch systems with chiral, time-reversal, or particle-hole symmetry

classification ❄️ cond-mat.mes-hall
keywords invariantstopologicalinvariantparticle-holesymmetryboundarybulkchiral
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We introduce $\mathbb Z_2$-valued bulk invariants for symmetry-protected topological phases in $2+1$ dimensional driven quantum systems. These invariants adapt the $W_3$-invariant, expressed as a sum over degeneracy points of the propagator, to the respective symmetry class of the Floquet-Bloch Hamiltonian. The bulk-boundary correspondence that holds for each invariant relates a non-zero value of the bulk invariant to the existence of symmetry-protected topological boundary states. To demonstrate this correspondence we apply our invariants to a chiral Harper, time-reversal Kane-Mele, and particle-hole symmetric graphene model with periodic driving, where they successfully predict the appearance of boundary states that exist despite the trivial topological character of the Floquet bands. Especially for particle-hole symmetry, combination of the $W_3$ and the $\mathbb Z_2$-invariants allows us to distinguish between weak and strong topological phases.

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