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CAMP:Interplay between the electronic band topology and phonons in Dirac materials

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Ion Garate, Sherbrook University
When
28 April 2015 from 4:00 PM to 5:00 PM
Where
339 Davey Laboratory
Contact Name
Chaoxing Liu
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Recent years have witnessed the discovery of novel topological phases in solids whose low-energy bulk excitations are Dirac fermions. Topological phases in these “Dirac materials” are characterized by nonzero integers (topological invariants), which manifest themselves through peculiar and robustly gapless states localized at the boundaries of the material. The unusual properties of topological surface (boundary) states have inspired numerous proposals for realizing low-dissipation magnetoelectronic devices and low-decoherence quantum computers.

Most theoretical studies to date have focused on closed quantum systems, wherein electrons are isolated from their environments.

Yet, in real crystals, electrons constitute open quantum systems coupled to various baths, of which the most ubiquitous are lattice vibrations (phonons).

The coupling between electrons and the bath can be strong enough that the topological invariants are changed.

Moreover, some of these changes could lead to potentially useful device applications.

In this talk, I will show that phonons can alter the band topology of narrow-gap Dirac insulators and semimetals, at both zero and nonzero temperature. Contrary to the common belief that increasing temperature always destabilizes topological phases, our results highlight instances in which phonons might induce topological surface states above a crossover temperature in a material that has a topologically trivial ground state. 

In the second part of the talk, I will turn the tables and discuss the back action of band topology on phonon properties.  Our results predict that the linewidths of certain phonon modes can display distinct signatures of the underlying electronic band topology.

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