Abstract-Strong coupling of collective intermolecular vibrations in organic materials at terahertz frequencies

Ran Damari, Omri Weinberg, Daniel Krotkov, Natalia Demina, Katherine Akulov, Adina Golombek, Tal Schwartz, Sharly Fleischer,

α-Lactose molecules in a tunable THz cavity. a Chemical structure of α-lactose. b A microscope image of an α-lactose crystallite. c Absorption coefficient of the α-lactose pellet obtained from the THz absorption measurement. The inset shows the fit of the measured absorption peak (blue line) to a lorentzian line-shape (black dashed line). d A sketch of the open THz cavity used in the experiments

https://www.nature.com/articles/s41467-019-11130-y

Several years ago, strong coupling between electronic molecular transitions and photonic structures was shown to modify the electronic landscape of the molecules and affect their chemical behavior. Since then, this concept has evolved into a new field known as polaritonic chemistry. An important ingredient in the progress of this field was the demonstration of strong coupling with intra-molecular vibrations, which enabled the modification of processes occurring at the electronic ground-state. Here we demonstrate strong coupling with collective, inter-molecular vibrations occurring in organic materials in the low-terahertz region (≲$\lesssim$1012 Hz). Using a cavity filled with α-lactose molecules, we measure the temporal evolution and observe coherent Rabi oscillations, corresponding to a splitting of 68 GHz. These results take strong coupling into a new class of materials and processes, including skeletal polymer motions, protein dynamics, metal organic frameworks and other materials, in which collective, spatially extended degrees of freedom participate in the dynamics.