Spins and dipoles inside superfluid helium nanodroplets

Expansion of helium gas through a cold nozzle generates a beam of very cold superfluid nanodroplets. If this beam passes through dilute atomic or molecular vapor, one or more “dopants” can become embedded in each droplet and are promptly cooled to their lowest vibrational and low rotational states. Very cold polar and magnetic dopants can then be strongly oriented by external fields, making it possible to perform beam deflection experiments on systems of various sizes and complexities (including assemblies that cannot be easily generated by other means). Stern-Gerlach and electric deflection measurements provide direct readout about the presence and magnitude of permanent dipole moments, and thereby about the formation of highly polar chains, charge-transfer complexes, and high-spin as well as antiferromagnetic configurations. The data also draw attention to the need for fuller understanding of the mechanisms and rates of spin relaxation inside the superfluid medium.

Speaker: Vitaly V. Kresin, University of Southern California