It is a 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 such as excitonic insulators [5,6] or Higgs modes in unconventional superconductors .
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. Focus could be either on novel Raman probes or transient second harmonic generation in the time domain to probe phase transitions in light driven systems. We will apply them to complex materials to reveal the above-mentioned dynamics and discuss their implications in strong collaboration with scientists throughout the institute working on equilibrium spectroscopy, in material science and theory.
The project student will learn how to handle the ultrashort pulse laser systems and the advanced nonlinear optics probing schemes including the required detection mechanisms. That will allow building their own experiment to probe these novel exciting phases in various materials that are in the joint research interest of the groups at the institute. Typical examples of phenomena under investigation (superconductivity, charge order, exciton-, spin- or phonon-dynamics, etc.) are found in the references.
 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 et al. Science Advances 4, eaap8652 (2018).
 D. Werdehausen et al. J. of Phys.: Cond. Mat. 30, 305602 (2018).
 B. Fauseweh et al. arxiv:1712.07989 (2017).