Displacive Excitation of Coherent Phonons in YBa2Cu3 O7: An Optical Evidence for the Van-Hove Singularity
Abstract
The amplitude of displacive excitation of coherent phonons ( DECP) in YBa2Cu3O7 observed in time-resolved spectroscopy increases by a very large factor of 15 between 20 K (below Tc) and 100 K (above Tc). Microscopic modelling of phonon excitation reveals that these amplitude changes of the A1g mode phonons are related to the existence of the Van-Hove singularity (VHS) below but very close to Fermi energy. PACS numbers: 78.47.+p, 74.25.Gz, 74.25.Jb, 71.15.Fv
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