Nonequilibrium Dynamics in Correlated Materials

In recent years, time-resolved spectroscopies have provided novel insights into the transient behavior of ordered phases, in which correlation effects play a prominent role. In these types of experiments, an intense and ultrashort laser pulse excites the electronic system far out of equilibrium. A second pulse probes the subsequent response of the system, as determined by the coupling between charge, spin and lattice. Non-equilibrium phenomena that are observed in these experiments include the generation of coherent phonons, the non-thermal destruction of charge-ordered states and the ultrafast quenching of magnetism.  More...

Bild zur NichtgleichgewichtsdynamikA coherent phonon mode in TaSe2 excited with 30 fs near-infrared laser pulses probed in a time-resolved ARPES using 22 eV photon pulses from a high-harmonic generation source.

Using time- and angle-resolved photoelectron spectroscopy (TRARPES) we probe transient changes in the electronic structure in order to gain insights into the non-equilibrium physics in charge-density wave materials and unconventional superconductors. The application of coherent femtosecond pulses in the extreme ultraviolet (XUV) spectral regime from a high-harmonic generation (HHG) source is the key for accessing electronic states at high momenta and large binding energies [1]. The project is result of a close collaboration with the group of Kai Rossnagel/Lutz Kipp. Examples of recent work include the measurement of extremely fast melting times of the excitonic insulator phase in 1T-TiSe2 [2], the classification of complex insulators via time-domain characterization of gap melting times [3], and the observation of an unexpected coupling between chemical potential and coherent phonons in iron pnictides [4]. The movie shows TRARPES data recorded during the ultrafast melting of a charge-ordered phase in 1T-TiSe2.

TRARPES data of ultrafast melting of a charge-ordered phase in 1T-TiSe2 [2];

[1] “Angle Resolved Photoemission Spectroscopy with a Femtosecond High Harmonic Light Source using a 2D Imaging Electron Analyzer“ S. Mathias, L. Miaja-Avila, M.M. Murnane, H. Kapteyn, M. Aeschlimann, and M. Bauer, Rev. Sci. Instr. 78, 083105 (2007). doi:10.1063/1.2773783

[2] “Collapse of long-range charge order tracked by time-resolved photoemission at high momenta“ T. Rohwer, S. Hellmann, M. Wiesenmayer, C. Sohrt, A. Stange, B. Slomski, A. Carr, Y. Liu, L. Miaja Avila, M. Kalläne, S. Mathias, L. Kipp, K. Rossnagel, M. Bauer; Nature 471, (2011) 490. doi:10.1038/nature09829

[3] “Time-domain classification of charge-density-wave insulators“ S. Hellmann, T. Rohwer, M. Kalläne, K. Hanff, C. Sohrt, A. Stange, A. Carr, M. M. Murnane, H. C. Kapteyn, L. Kipp, M. Bauer, K. Rossnagel; Nat. Commun. 3 (2012) 1069. doi:10.1038/ncomms2078

[4] “Ultrafast modulation of the chemical potential in BaFe2As2 by coherent phonons“ L. X. Yang, G. Rohde, T. Rohwer, A. Stange, K. Hanff, C. Sohrt, L. Rettig, R. Cortes, F. Chen, D. L. Feng, T. Wolf, B. Kamble, I. Eremin, T. Popmintchev, M. M. Murnane, H. C. Kapteyn, L. Kipp, J. Fink, M. Bauer, U. Bovensiepen, K. Rossnagel; Phys. Rev. Lett. 112 (2014) 207001. doi:10.1103/PhysRevLett.112.207001

Funding: DFG, project BA 2177/9-1