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 opens new avenues in controlling physical properties and designing new functionalities.
I will show how we investigate different scenarios like the balancing between competing phases triggered by ultrashort light pulses or possibilities of dynamical stabilization of new states of matter in periodically driven light fields. In particular I will review the remarkable possibilities to induce superconductivity in high temperature cuprate superconductors , novel ways controlling effective interactions in molecular crystals [2,3] and the avenues to probe collective coherent order and its couplings in an excitonic insulator .
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 D. Werdehausen et al. Science Advances 4, eaap8652 (2018).