Seminars Archive

Pathway selective multidimensional spectroscopy

Abstract
Ultra-fast experiments are often performed in two-pulse pump-probe geometry, where the dynamics of the system response reveals the details of the photo-induced processes. However, as several contributions or pathways sum up to give the pump-probe signal, it can be difficult to isolate the quantum coherences excited during the light-matter interaction with this approach. Here we show that a narrowband and phase-resolved four-wave mixing experiment, or pathway-selective 2D electronic spectroscopy, can be used to selectively study quantum coherences in a variety of systems. This powerful spectroscopic tool allows, for example, to disentangle excited from ground state coherences in natural pigment-protein molecular complexes and to reveal the mixed electronic-vibrational nature of these excitations. In addition, we demonstrate that the prototypical cuprate LSCO displays a quantum coherent response, involving states around the Fermi level, that outlasts the pulse duration by several hundreds femtoseconds at room temperature. Characterising the cuprates with 2D pathway-selective ultra-fast spectroscopy might reveal the dressing of the charge excitations in these and other strongly correlated systems.