Photo-Induced Insulator-Metal Transition in a Low Dimensional Organic Conductor, Observed by Ultrafast Electron Diffraction
October 29th, 2019 HEINRICH SCHWOERER Max Planck Institut für Struktur und Dynamik der Materie, Hamburg

Among functional organic materials, low dimensional molecular crystals represent an intriguing class of solid states due to their tunable electronic, magnetic and structural ground states. We report on the collective ultrafast atomic motions at the photo-induced insulator-metal Peierls transition of Cu(Me,Br-Dicyanoquinonediimine)2 single crystals. Ultrafast electron diffraction experiments reveal the photo-induced lifting of the insulating phase to happen within 2 ps in the entire crystal volume with an external quantum efficiency of conduction band electrons per absorbed photon of larger than 20. The phase transition is guided by specific intramolecular motions. However, only an additional internal volume expansion, corresponding to an internal pressure relief, allows to optically lock the metallic state for long times. The identification of the microscopic molecular pathways that optically drive the structural Peierls transition in Cu(DCNQI)2 highlights the tailored response to external stimuli available in these complex functional materials, a feature enabling high-speed optical sensing and switching with outstanding signal responsivity.

These ultrafast structural dynamics have been observed by a time resolved electron diffraction experiment. I will introduce its basic concepts, specifications, limitations and perspectives.

Seminar, October 29, 2019, 11:00. ICFO’s Seminar Room

Hosted by Prof. Jens Biegert