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Clifford Bowers - The Bowers research group specializes in developing new methods of detection of nuclear magnetic resonance which exploit couplings of electrons and nuclei in optical and electronic transport processes. A broad range of applications are facilitated by these new methods, including low-dimensional quantum systems such as semiconductor quantum wells and other multilayer thin film structures, metal films, chemically active surfaces, gas clathrates, and biological macromolecules.

One of the primary methods employed by us is known as spin exchange optical pumping. In this method, a nonequilibrium electron spin polarization of the ground or excited state can be prepared by optical excitation according to the selection rules for optical transitions. The electron spin polarization can be transferred to the nuclei via hyperfine relaxation. We are conducting spin exchange optical pumping experiments in gases and solid state systems. Spin exchange optical pumping with rubidium vapor can produce large quantities of highly polarized xenon-129 or helium-3. In our lab, 50,000 fold NMR signal enhancements have been observed, corresponding to a xenon-129 spin polarization of about 50%. This NMR signal enhancement has been applied
to the study of binding sites in proteins and to the mechanism of the reaction of xenon with ice crystals to form xenon clathrate hydrate. Hyperpolarized xenon-129 is also being employed in microimaging of materials.

Spin polarization phenomena in nanostructured solid state materials is another focus of our research. Ultra-sensitive electronic transport detection methods for ESR and NMR have been combined with spin exchange optical pumping and dynamic nuclear polarization enhancement of spin polarization. Bowers has demonstrated the ability to detect as few as 10,000 spins for a 1 Gauss ESR line width using electrically detected ESR in GaAs/AlGaAs multi-quantum wells. Using this remarkable detection method it was demonstrated that optical pumping can change the Zeeman energy of the quantum confined electrons, enabling the hyperfine coupling between nuclei and the electrons in the two-dimensional electron system to be measured for the first time. Bowers and co-workers also demonstrated that the nuclear spin polarization can be directly detected via the magnetoconductance in the quantum Hall effect. This previously unobserved effect was employed to measure the number of spin flips associated with skyrmion-antiskyrmion excitations of the 2DES near the unity filling factor. Such measurements are of fundamental interest to the condensed matterphysics community.

Other areas of interest of the Bowers group include development of solid state NMR techniques, and applications of conventional NMR methods in studies
of catalysts and thin-film materials. These applications usually involve collaborative work with other research groups in UF's Chemistry Department and elsewhere.