Direct observation of Higgs mode oscillations in the pump-probe photoemission spectra of electron-phonon mediated superconductors

A. F. Kemper,1,2,* M. A. Sentef,3 B. Moritz,4,5 J. K. Freericks,6 and T. P. Devereaux4,7 1Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA 2Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA 3HISKP, University of Bonn, Nussallee 14-16, D-53115 Bonn, Germany 4Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA 5Department of Physics and Astrophysics, University of North Dakota, Grand Forks, North Dakota 58202, USA 6Department of Physics, Georgetown University, Washington, D.C., 20057, USA 7Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA (Received 23 March 2015; published 30 December 2015)