CTCP Seminar : “Quantum Spin Liquid as incompressible liquid of electrons” by Prof Yi ZHOU Monday, February 10, 2025, 5:00pm, LE8, Library Extension Building, HKU

An alternative to the “standard” quantum spin liquid model, which was constructed as a gauge theory, will be presented. This new framework is a Landau-type effective theory. We will explore both quasiparticle excitations and collective modes, along with their physical implications.

HKIQST Seminar “Nonequilibrium and nonlinear terahertz spectroscopy study on Higgs modes in conventional and unconventional superconductors” by Prof Nan-Lin WANG on Wednesday, January 15, 2025, 3:00 pm | CYPP3

We present recent progress in exploring the detection of superconducting collective modes
in NbN, MgB2, and YBa2Cu3O6+x using innovative terahertz spectroscopy techniques.
Transient Higgs oscillations and a higher-order nonlinear light-Higgs mode coupling effect
were detected in NbN superconductors. In MgB2, the Higgs mode contribution from the dirty
3D pi-band and the Leggett mode contribution were identified. In YBCO samples, a beat
pattern in the terahertz signal revealed a coupling effect between the Higgs mode and the
mode developed below T*, indicating the pseudogap phase may be a distinct order, not a
precursor to superconductivity. This strong coupling effect provides fresh insights into
superconductivity and the pseudogap.