Observation of photon-nucleus angular-momentum transfer in the strong-field breaking of molecules

The photon-electron angular-momentum transfer is intrinsic and overwhelmingly important in light-molecule interaction. However, the photon-nuclei angular-momentum transfer is seldom observed because of the very large inertial moment and the very small dipole of nuclei as compared to those of the electron. Here, we report the theoretical and experimental observation of the transfer of the spin angular momentum of the photon into the nuclear orbital angular momentum of a molecule. This spin angular-momentum transfer is revealed by carefully examining the emission direction of the ejected proton from the breaking H2 molecule, which deviates from the initial orientation of the molecular axis. The deviation of the emission direction of the nuclear fragments from the molecular axis depends on its kinetic energy and the ellipticity of the driving laser field, which is confirmed in our numerical simulations.