BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Spectroscopic signatures of collective modes in superconductors - 
 Lara Benfatto\, University of Rome\, La Sapienza
DTSTART:20141016T131500Z
DTEND:20141016T141500Z
UID:TALK53961@talks.cam.ac.uk
CONTACT:Dr G Moller
DESCRIPTION:The formation of the superconducting state leads to the appear
 ance of two\ncollective modes associated with the amplitude and phase fluc
 tuations of\nthe SC order parameter. A direct observation of these two mod
 es is usually\nelusive\, since in a standard BCS superconductor they coupl
 e weakly to the\nspectroscopic observables\, and they are overdamped by qu
 asiparticle\nexcitations. However\, whenever these two conditions are modi
 fied by\nadditional perturbations new remarkable effects can show up. Here
  I discuss\ntwo paradigmatic cases suggested by recent experiments in conv
 entional\nsuperconductors. The first example is the visibility of phase fl
 uctuations\nin a strongly disordered superconductor: we show that phase mo
 des become\noptical active in the presence of disorder\, and their contrib
 ution piles up\nbelow the optical gap due to quasiparticle excitations\, a
 s probed recent by\nmicrowave spectroscopy in conventional superconductors
  near the\nsuperconductor-to-insulator transition.The second example is th
 e visibility\nof Higgs (amplitude) mode in the superconducting state forme
 d after a\ncharge-density-wave (CDW) transition. We show that the pre-exis
 ting CDW gap\npushes the quasiparticle continuum away from the Higgs pole\
 , making it a\ntrue\, undamped excitation. This reflects in a strong reson
 ance in the Raman\nresponse\, where the Higgs visibility is provided by th
 e soft CDW phonon\, as\nsuggested long ago for NbSe2.\n
LOCATION:TCM Seminar Room\, Cavendish Laboratory
END:VEVENT
END:VCALENDAR