#Stefan kaiser essntia free
While both free and driven Higgs oscillations have been demonstrated in s-wave superconductors, the Higgs mode of d-wave superconductors is more complex. In the latter scenario, the 2ω oscillation of the condensate interacts with the driving field A( ω), leading to sum frequency generation or third harmonic generation (THG), which is resonantly enhanced when 2 ω = 2Δ( T) 10, 13. The resulting free (driven) Higgs oscillation manifests itself in terahertz transmissivity as an oscillation at 2Δ (2 ω). Alternatively, it could also be periodically driven at 2 ω through nonlinear coupling between the electromagnetic vector potential A( ω) and the superconducting condensate 10, 11, 12. Specifically, free oscillations of the Higgs mode, with its characteristic frequency of 2Δ, can be launched by an ultrashort terahertz pulse quenching the free energy of the order parameter 9. Novel methods for exciting and detecting the superconducting Higgs mode were also demonstrated using ultrafast terahertz techniques in the meantime 9, 10.
Recently, it was proposed that the Higgs mode may reveal the superconducting gap symmetry and multiplicity 4, 5, 6, unveil coupled collective modes 7, or explain aspects of light-induced superconductivity 8. Experimental detection of the Higgs mode has also been hampered by its lack of electric and magnetic dipole moments in most superconductors. However, their significance to superconductivity has been more slowly appreciated.
In superconductors, discussions about the Higgs mode and the Higgs mechanism precede those in high-energy physics 2, 3. Nature Communications volume 11, Article number: 1793 ( 2020)įor field theories with U(1) continuous symmetry and respecting Lorentz invariance or particle-hole symmetry, spontaneous symmetry breaking gives rise to an order parameter with two orthogonal collective modes: the Goldstone mode along the azimuthal direction, and the Higgs mode along the radial direction 1. Phase-resolved Higgs response in superconducting cuprates
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