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In 1964 the theoretical work of Higgs, Guralnik, Hagen, Kibble, Brout, and Englert led to the prediction that, as a consequence of the coupling bet- ween matter currents and gauge particles, the gauge particles can acquire a non-zero mass. As Higgs phrased it, „this phenomenon is just the relati- vistic analog of the plasmon phenomenon to which Anderson has drawn attention: that the scalar zero-mass excitations of a superconducting neu- tral Fermi gas become longitudinal plasmon modes of finite mass when the gas is charged.“ A superconducting gap has collective oscillations of its amplitude –equi- valent to the Higgs particle- and of its phase. As shown by Anderson in 1958, the longitudinal and transverse oscillations of the superconducting condensate coupled to the electromagnetic field now acquire a finite mass, which is seen experimentally in the energy-momentum dispersion. In cer- tain superconductors two or more condensates coexist. Weak coupling bet- ween the condensates then gives rise to the so-called Leggett-exciton, and the coupling to the electromagnetic field makes that two or more massive photon-branches coexist. These and many other phe- nomena in elementary par- ticles and condensed matter are marvelous by the beau- ty and simplicity of the prin- ciples uniting them, despite conditions and energy sca- les being so vastly different.

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Dirk van der Marel, University of Geneva
HS III
Contact: not specified