[QC/solid state] Hyperfine Structure and Nuclear Hyperpolarization Observed in the Bound Exciton Luminescence of Bi Donors in Natural Si

http://prl.aps.org/pdf/PRL/v104/i13/e137402

As the deepest group-V donor in Si, Bi has by far the largest hyperfine interaction and also a large I=9/2 nuclear spin. At zero field this splits the donor ground state into states having total spin 5 and 4, which are fully resolved in the photoluminescence spectrum of Bi donor bound excitons. Under a magnetic field, the 60 expected allowed transitions cannot be individually resolved, but the effects of the nuclear spin distribution, -9/2≤I_z≤9/2, are clearly observed. A strong hyperpolarization of the nuclear spin towards I_z=-9/2 is observed to result from the nonresonant optical excitation. This is very similar to the recently reported optical hyperpolarization of P donors observed by EPR at higher magnetic fields. We introduce a new model to explain this effect, and predict that it may be very fast.