Abstract
We present a combined experimental and theoretical study of cold collisions between bismuth and helium atoms in strong magnetic fields and demonstrate that the spin-orbit interaction coupling between different nonrelativistic states of Bi leads to rapid Zeeman relaxation. The Zeeman relaxation of Bi in the ground electronic state is found to be very efficient due to the admixture of electronic excited states which show an interaction anisotropy due to their nonzero electronic orbital angular momentum. Our results indicate that dense ensembles of heavy relativistic atoms will generally be unstable in magnetic traps due to significant spin relaxation induced by spin-orbit interactions.
Highlights
Inelastic collisions between paramagnetic atoms and noble-gas atoms in a magnetic field have long been of significant interest for experiments in optical pumping1͔, precision measurement and precision magnetometry2,3͔, nuclear physics4,5͔, and magnetic resonance imaging6͔
We present a combined experimental and theoretical study of cold collisions between bismuth and helium atoms in strong magnetic fields and demonstrate that the spin-orbit interaction coupling between different nonrelativistic states of Bi leads to rapid Zeeman relaxation
Our results indicate that dense ensembles of heavy relativistic atoms will generally be unstable in magnetic traps due to significant spin relaxation induced by spin-orbit interactions
Summary
Inelastic collisions between paramagnetic atoms and noble-gas atoms in a magnetic field have long been of significant interest for experiments in optical pumping1͔, precision measurement and precision magnetometry2,3͔, nuclear physics4,5͔, and magnetic resonance imaging6͔. We present a study of a very different system: cold collisions of helium and bismuththe heaviest stable element with a half-filled p shelland discuss how measurements of elastic scattering and collision-induced Zeeman relaxation at low temperatures can provide a probe of the spin-orbit interaction in heavy atoms. Calculations have shown that the nominally S ground state of bismuth has only ϳ57% S character24,25͔; contributions to the ground state mixed in by spin-orbitSOcoupling include terms with nonzero angular momentum. These non-S terms introduce electronic interaction anisotropy with helium. We observe the effects of this anisotropy in Bi experimentally by observing angular momentum reorientation in collisions with cold helium gas
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