Stefan KAISER
When a continuous symmetry of a physical system is spontaneously broken, two types of collective modes emerge: the amplitude and phase modes of the order-parameter fluctuation. For superconductors, the amplitude mode is the so called “Higgs mode”, the condensed-matter analogue of a Higgs boson in particle physics.
Recent advances in THz technology allow to excite such Higgs modes in superconductors. I will review how this possibility can be extended into a “Higgs Spectroscopy” that reveals the internal structure and dynamics of a superconducting condensate. That becomes in particular interesting for unconventional superconductors where a complicated interplay of competing or intertwined orders obscures the view on the possible pairing mechanism.
I will discuss how a phase resolved nonlinear THz spectroscopy paves the way to such a Higgs spectroscopy directly probing the collective condensate dynamics and exposing its coupling to external collective modes or quasiparticle excitations.
[2] Lukas Schwarz et al., Classification and characterization of nonequilibrium Higgs modes in unconventional superconductors, Nature Commun. 11, 287 (2020).
[3] Hao Chu et al., Fano interference of the Higgs mode in cuprate high-Tc superconductors, arXiv:2109.09971