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.