Abstract
Despite the formal analogy with the Higgs particle, the amplitude fluctuations of the order parameter in weakly coupled superconductors do not identify a real mode with a Lorentz-invariant dynamics. Indeed, its resonance occurs at , which coincides with the threshold for quasiparticle excitations that spoil any relativistic dynamics. Here we investigate the fate of the Higgs mode in the unconventional case where becomes larger than , as due to strong coupling or strong disorder. We show that also in this situation, the amplitude fluctuations never identify a real mode at , since such a “bosonic” limit is always reached via strong mixing with the phase fluctuations, which dominate the low-energy part of the spectrum. Our results have direct implications for the interpretation of the subgap optical absorption in disordered superconductors.
- Received 8 April 2015
DOI:https://doi.org/10.1103/PhysRevLett.115.157002
© 2015 American Physical Society