It is well known fact that various phase transitions in condensed matter can by triggered by external parameters such as temperature, pressure, electric field or magnetic field. Finding systems that show phase transitions triggered by external stimulation of light became a particular interesting field of research.
Advanced nonlinear optical methods such as ultra-broad band pump-probe spectroscopy open new ways of controlling ultrafast dynamics in complex solid-state materials on unprecedented timescales. In quantum materials, finding new ways of manipulating the complex interplay of electronic phases or effectively tuning electronic interactions opens new avenues in controlling physical properties and designing new functionalities.
Remarkable possibilities are light-induced superconductivity in high temperature cuprate superconductors [1-3] or doped fullerides K3C60 , or the identification of coherent condensates in complex quantum materials [5-7].
We work on methods to investigate and characterize both the transient quasi-particle dynamics and light-driven interactions in such systems with various types of time-resolved spectroscopies.
In the scope of the project the applicant will learn basic principles of these spectroscopies (with focus on a specific technique based on interest) and apply them to complex materials to reveal the above-mentioned dynamics and discuss their implications in strong collaboration with equilibrium spectroscopy, the material scientists and theory (all well represented within the institute).
 D. Fausti et al. Science 331, 189 (2011).
 S. Kaiser et al. Phys. Rev. B 89, 184515 (2014).
 W. Hu et al. Nature Materials 13, 705 (2014).
 M. Mitrano et al. Nature 530, 461 (2016).
 D. Werdehausen, “Non-Equilibrium Higgs-Phonon Coupling in the Excitonic Insulator Ta2NiSe5”, Master thesis (2016).
 S.Y. Agustsson, “Ultrafast Exciton Dynamics Revealing a Coherent Condensate in the Excitonic Insulator Ta2NiSe5”, Master thesis (2016).
 D. Werdehausen et al. arxiv:1611.01053 (2016).