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Orbital Angular Momentum of Chiral Superfluids: New Understandings

Speaker:Prof. Huang Wen
Affiliation:Shenzhen Institute for Quantum Science and Engineering,
Southern University of Science and Technology
Date:November 7, 2019 (Thursday)
Time:11:00 a.m.
Venue:Room 522, 5/F, Chong Yuet Ming Physics Building, HKU


Cooper pairs in chiral superfluids carry quantized units of orbital angular momentum (OAM). Predictions of the total OAM of a chiral superfluid differ by several orders of magnitude, and they constitute the so-called angular momentum paradox initially raised some 50 years ago. In this talk, I will present recent developments in our understanding of the problem. Against our intuition, the total OAM is found to essentially vanish for all two-dimensional non-p-wave BCS chiral superfluids (such as chiral d+id) confined in a sharp circular geometry. The BEC chiral superfluids, by contrast, carry the intuitively expected total OAM as if all Cooper pairs contribute additively. I will show that these phenomena are all edge physics resultant from the translation symmetry breaking due to the presence of a boundary. In particular, the surprising vanishing of the OAM in the BCS limit will be explained from the perspective of the current-carrying topological chiral edge states, as well as a phenomenological Ginzburg-Landau theory. Some differences from the previous theories will also be discussed.

Refs: [1] WH, E. Taylor, and C. Kallin, Phys. Rev. B 90, 224519 (2014); [2] Y. Tada, W. Nie, and M. Oshikawa, Phys. Rev. Lett. 114, 195301 (2015); [3] WH, W. Nie, and H. Yao, in preparation.

Coffee and tea will be served 20 minutes prior to the seminar.

Anyone interested is welcome to attend.