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Add to Calendar 4/8/2019 12:00 pm 4/8/2019 America/Chicago Institute for Condensed Matter Theory Seminar: "Topological revamp of band theory: from period-multiplied Bloch oscillations to topological photonic crystals" DESCRIPTION:

Bloch oscillations originate from the translational symmetry of crystals. These oscillations occur with a fundamental period that a semiclassical wave packet takes to traverse a Brillouin-zone loop. We introduce a new type of Bloch oscillations whose periodicity is an integer multiple of the fundamental period, as has been observed in cold-atomic experiments. The period multiplier is an invariant protected by the space groups of crystals, and has two complementary explanations: one from quantized Berry-Zak phases (acquired from adiabatic transport of Bloch functions in momentum space), and the other from the real-space distribution of Wannier functions. Building upon questions of what symmetries can be imposed on Wannier functions, we elucidate how obstructions to symmetric Wannier functions are realized in topological band insulators and photonic crystals. In particular, it is shown that an existing photonic crystal – that is touted to have robust Dirac-like surface states [Nature, 565, 622] – actually exhibits a less robust, “fragile” topology.

 

References:

Phys. Rev. B 98, 024310 (2018)

Phys. Rev. B 98, 184305 (2018)

 

\n\nSPEAKER: Aris Alexandradinata, University of Illinois Urbana Champaign
190 ESB false

Institute for Condensed Matter Theory Seminar: "Topological revamp of band theory: from period-multiplied Bloch oscillations to topological photonic crystals"

Speaker Aris Alexandradinata, University of Illinois Urbana Champaign
Date: 4/8/2019
Time: 12 p.m.
Location: 190 ESB
Sponsor: The Physics Department
Event Type: Seminar/Symposium
 

Bloch oscillations originate from the translational symmetry of crystals. These oscillations occur with a fundamental period that a semiclassical wave packet takes to traverse a Brillouin-zone loop. We introduce a new type of Bloch oscillations whose periodicity is an integer multiple of the fundamental period, as has been observed in cold-atomic experiments. The period multiplier is an invariant protected by the space groups of crystals, and has two complementary explanations: one from quantized Berry-Zak phases (acquired from adiabatic transport of Bloch functions in momentum space), and the other from the real-space distribution of Wannier functions. Building upon questions of what symmetries can be imposed on Wannier functions, we elucidate how obstructions to symmetric Wannier functions are realized in topological band insulators and photonic crystals. In particular, it is shown that an existing photonic crystal – that is touted to have robust Dirac-like surface states [Nature, 565, 622] – actually exhibits a less robust, “fragile” topology.

 

References:

Phys. Rev. B 98, 024310 (2018)

Phys. Rev. B 98, 184305 (2018)

 

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