Martin Lisowski

Femtosecond dynamics of electronic states in the Mott insulator 1T-TaS2 by time resolved photoelectron spectroscopy

Photoexcitation of the Mott insulator 1T-TaS2 by an intense laser pulse leads to an ultrafast transition toward a gapless phase. Besides the collapse of the electronic gap, the sudden excitation of the charge density wave (CDW) mode results in periodic oscillations of the electronic states. We employ time resolved photoelectron spectroscopy to monitor the rich dynamics of electrons and phonons during the relaxation toward equilibrium. The qualitative difference between the oscillatory dynamics of the CDW and the monotonic recovery of the electronic gap proves that 1T-TaS2 is indeed a Mott insulator. Moreover the quasi-instantaneous build-up of mid gap states is in contrast with the retarded response expected from a Peierls insulating phase. Interestingly, the photoinduced electronic states in the midgap spectral region display a weak resonance that is reminiscent of a quasiparticle peak.

Non-equilibrium spin-dynamics of Gd(0001) studied by time-resolved SHG and magnetic linear dichroism in 4f core-level photoemission

Spin dynamics following short pulse laser excitation was studied for Gd(0001). The dynamics of Gd valence-spins differs fundamentally from that in 3d ferromagnets. This is attributed to interaction between Gd 5d and 4f magnetic moments and the large 4f spin-lattice interaction time of 80 ps deduced from laser-pump synchrotron-probe 4f photoemission

Time Resolved Photoemission of Correlated Electron Materials

Using femtosecond time-resolved photoemission from solids we study the mechanism of the laser-driven ultrafast insulator to metal transition in the Mott insulator TaS2and the dynamics of electron-phonon coupling in high-Tc superconductors.