| Condensed Matter
Thursday, December 5, 2019
Physics Building, Room 313
Note special time.
Note special room.
Professor Yi Li
[Host: Dima Pesin]
Johns Hopkins University
"Monopole Superconductivity and Density-Wave Order in Weyl Semi-metals"
Although the existence of magnetic monopoles is admitted by the fundamental laws, the real monopoles in nature remain elusive. Nevertheless, variations of monopoles appear in realistic condensed matter systems, from quantum Hall effects to topological superconductivity, which spur a race to discover new exotic topological phases of matter. In this talk, we will present a dramatic effect arising from topological Fermi surfaces -- a novel topological class of superconductivity and density-wave orders: When the ordered pairs acquire non-trivial two-particle Berry phases, their pairing phases cannot be globally well-defined in the momentum space. Therefore, the conventional description of superconducting pairing symmetries in terms of spherical harmonics (e.g. s-, p-, d-waves) ceases to apply. Instead, they are characterized by topologically protected nodal gap functions represented by monopole harmonic functions. This so-called “monopole harmonic order” is expected to be realized and detected in Weyl semimetal materials.
Friday, December 6, 2019
Physics Building, Room 204
[Host: Simonetta Liuti]
University of Illinois at Urbana-Champaign
"Exploring the Nucleon Sea"
Direct experimental evidence for point-like constituents in the nucleons
was first found in the electron deep inelastic scattering (DIS) experiment.
The discovery of the valence and sea quark structures in the nucleons
inspired the formulation of Quantum Chromodynamics (QCD) as the gauge field
theory governing the strong interaction. A surprisingly large asymmetry
between the up and down sea quark distributions in the nucleon was observed
in DIS and the so-called Drell-Yan experiments. In this talk, I discuss the
current status of our knowledge on the flavor structure of the nucleon sea.
I will also discuss the progress in identifying the "intrinsic" sea
components in the nucleons. Future prospect for detecting some novel
sea-quark distributions will also be presented.