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I will examine the role of topological ideas in understanding semimetals, gapless phases whose Fermi surfaces may be shrunk to isolated point nodes. First, I will review the theory of ‘Weyl semimetals’ that arise from accidental degeneracies in 3D crystals, and explore the consequences of the resulting band topology. I will show that the interplay of crystal symmetry and topology can aid in identifying “filling-enforced” semimetals, including in strongly correlated systems such as heavy fermion materials. I will also sketch how the topological underpinnings of these gapless phases may be probed experimentally via transport and spectroscopy, and through numerical simulations of their descendant gapped phases. References: Nat. Phys. 9, 299 (2013); PRX 4, 031035 (2014) ; PRX 5, 041046 (2015); PRB 94, 125122 (2016); arXiv:1508.01546, 1609.04023.

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Sid Parameswaran, UC Irvine
Seminar Room 0.03, ETP
Contact: Simon Trebst