Amplitude or Higgs modes in d-wave superconductors

Yafis Barlas; C. M. Varma

doi:10.1103/PhysRevB.87.054503

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Amplitude or Higgs modes in d-wave superconductors

Yafis Barlas, C. M. Varma

DOI 10.1103/PhysRevB.87.054503 · Physical Review B

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Abstract

In Lorentz-invariant systems spontaneously broken gauge symmetry results in three types of fundamental excitations: density excitations, Higgs bosons (amplitude modes), and Goldstone bosons (phase modes). The density and phase modes are coupled by electromagnetic interactions while the amplitude modes are not. In s-wave superconductors, the Higgs mode, which can be observed only under special conditions, has been detected. We show that unconventional d-wave superconductors, such as the high-temperature cuprate superconductors, should have a rich assortment of Higgs bosons, each in a different irreducible representation of the point-group symmetry of the lattice. We also show that these modes have a characteristic singular spectral structure and discuss conditions for their observability.