Hosted by: Jonathan Rameau

Optical excitations in solid materials decay typically on femto- to picosecond time scales due to interactions which lead to a redistribution of the excess energy among the electronic, the lattice, and the spin subsystem, before final dissipation. We perform pump-probe experiments in order to analyze these excitations and the action they generate through their relaxation directly in the time domain. In this talk time- and angle-resolved photoemission (tr-ARPES) results which probe the excited state with energy and momentum sensitivity on complex materials like charge density wave compounds [1] and high temperature superconductors [2,3] will be discussed. In the prototype charge density wave material RTe3 (R=Ho, Tb, Dy) we obtained a momentum dependent analysis of the time dependent gap function (k,t) which sheds lights on the amplitude mode and the interaction responsible for the charge density wave formation. In the iron based superconductor material BaFe2As2 the optical excitation induces oscillations in the chemical potential linked to the coherent A1g phonon which modulates the pnictogen height and electronic correlations. In the cuprates pump-induced changes are observed below and above Tc. We obtained evidence for considerable photo-doping effects based on transient changes in the Fermi momentum kF upon optical excitation. Remarkably, the observed changes follow predictions based on chemical doping, which suggests time- and angle-resolved photoemission as a novel method to differentially probe the Fermi surface of complex materials. [1] L. Rettig, J.-H. Chu, I. R. Fisher, U. Bovensiepen, M. Wolf, Faraday Discuss. 171, 1 (2014). [2] J. Rameau, S. Freutel, L. Rettig, I. Avigo, M. Ligges, Y. Yoshida, H. Eisaki, J. Schneeloch, R. D. Zhong, Z. J. Xu, G. D. Gu, P. D. Johnson, U. Bovensiepen, Phys. Rev. B 89, 115115 (2014). [3] L. X. Yang, G. Rohde, T. Rohwer, A. Stange, K. Hanff, C