Theory Seminar: Topology of the Fermi sea: ordinary metals as topological materials
Pok Man Tam, University of Pennsylvania
Theory Seminar at MPQ lecture hall and zoom
Wednesday, February 15th, 15:30pm (MEZ)
It has long been known that the quantum ground state of a metal is characterized by an abstract manifold in the momentum space called the Fermi sea. Fermi sea can be distinguished topologically in much the same way that a ball can be distinguished from a donut by counting the number of holes. The associated topological invariant, i.e. the Euler characteristic (χ_F), serves to classify metals. Here I will survey two recent proposals relating χ_F to experimental observables, namely: (i) equal-time density/number correlations, and (ii) Andreev state transport along a planar Josephson junction. Particularly, from the perspective of quantum information, I will explain how multipartite entanglement in real space can probe the Fermi sea topology in momentum space. Our works not only suggest a new connection between topology and entanglement in gapless quantum matters, but also propose accessible experimental platforms to extract the topology in ordinary metals.
This talk will be based on the following two works:
 P. M. Tam, M. Claassen, C. L. Kane, Phys. Rev. X 12, 031022 (2022)
 P. M. Tam and C. L. Kane, arXiv:2210.08048