Andrea Cavalleri

Abstract:

Time- and angle-resolved photoemission spectroscopy directly enables observation of electron dynamics in condensed matter. Using EUV high harmonic probe extends the observation window in energy and momentum. Tuneable mid-infrared pumping allows control of excitation mechanisms.Research in Optical Sciences © OSA 2014.

Abstract:

Nonlinear lattice excitation in YBa2Cu3O6.5 has been shown recently to transiently induce signatures of superconducting coherence up to room temperature. Here, we present ultrafast x-ray diffraction measurements used to determine the corresponding atomic structure. © 2014 OSA.

Abstract:

We have used time- and angle-resolved photoemission spectroscopy (tr-ARPES) to assess the influence of many-body interactions on the Dirac carrier dynamics in graphene. From the energy-dependence of the measured scattering rates we directly determine the imaginary part of the self-energy, visualizing the existence of a relaxation bottleneck associated with electron-phonon coupling. A comparison with static line widths obtained by high-resolution ARPES indicates that the dynamics of photo-excited carriers in graphene are solely determined by the equilibrium self-energy. Furthermore, the subtle interplay of different many-body interactions in graphene may allow for carrier multiplication, where the absorption of a single photon generates more than one electron-hole pair via impact ionization. We find that, after photo-excitation, the number of carriers in the conduction band along the ΓK-direction keeps increasing for about 40 fs after the pump pulse is gone. A definite proof of carrier multiplication in graphene, however, requires a more systematic study, carefully taking into account the contribution of momentum relaxation on the measured rise time.