December 2018
Abstracts of the QSIT Lunch Seminar, Thursday, December 6, 2018
39K2 Long-range Rydberg molecules bound by electron-atom scattering in the regime of strong hyperfine-induced mixing
Michael Peper – Molecular Physics and Spectroscopy (Merkt group), ETH Zurich
Gas-phase spectra of atomic and molecular Rydberg states show shifts and broadenings that are dependent on the gas pressure. These shifts and broadenings can be attributed to the Rydberg electron interacting with ground-state particles within the Rydberg electron's orbit. This interaction can be treated using scattering theory, which predicts oscillatory interaction potentials between the Rydberg atom and ground-state atoms. In case of a negative s-wave scattering length the interaction potentials may support bound states of diatomic molecules, called long-range Rydberg molecules. For alkali metal atoms, the triplet s-wave scattering length is negative whereas the singlet scattering length is very small or even positive. However, the hyper ne interaction in the ground-state atom induces a mixing of singlet and triplet scattering channels, entangling the nuclear spin of the ground-state atom with the molecular electronic spin.
I will present spectroscopic studies using ultraviolet and millimeter-wave radiation of the formation and dynamics of long-range Rydberg molecules in an ultracold potassium gas. These studies reveal a regime where strong hyperfine-induced mixing allows for a remote
manipulation of the internal state of the perturbing ground-state atom.
Investigating Long Range Vibrations in Nanocrystal Solids
Maximilian Jansen – Institute for Electronics (Wood group), ETH Zurich
The assembly of semiconductor nanocrystals (NCs) into conductive and ordered solids is of interest for a wide range of electronic applications. Control of the constituent NCs allows for a facile tuning of the NC solids electronic, structural and thermal properties. An important contributor to the thermal characteristics is the vibrational spectrum of the NC solid. We expect inter-particle vibrations, analogous to phonons on the atomic level, to be of importance for long range heat transport. These vibrational excitations involve multiple NCs and are of a longer length scale than any other vibration type in the NC solid. By implementing a three-dimensional mass-spring model, we demonstrate the behavior of these long-range vibrations as an effect of mass-spring disorder. Using the model we explore the parameter space of particle size and ligand type and their effect on the energy regime of the inter-particle vibrations. Additionally, we experimentally confirm their existence through inelastic neutron scattering and determine their characteristic energy scale and density. We successfully demonstrate that the energy regime of these inter-particle excitations can be engineered by varying particle size and ligand type of the NCs.