High resolution solid state NMR in paramagnetic metal-organic frameworks.

We study the metal-organic framework (MOF) ZIF-67 with 1H and 13C nuclear magnetic resonance (NMR). In addition to the usual orbital chemical shifts, we observe spinning sideband manifolds in the NMR spectrum due to hyperfine interactions of the paramagnetic cobalt with 1H and 13C. Both orbital and paramagnetic chemical shifts are in good agreement with values calculated from first principles, allowing high-confidence assignment of the observed peaks to specific sites within the MOF. Our measured resonance shifts, line shapes, and spin lattice relaxation rates are also consistent with calculated values. We show that molecules in the pores of the MOF can exhibit high-resolution NMR spectra with fast spin lattice relaxation rates due to dipole-dipole couplings to the Co2+ nodes in the ZIF-67 lattice, showcasing NMR spectroscopy as a powerful tool for identification and characterization of "guests" that may be hosted by the MOF in electrochemical and catalytic applications.

Linear Hyperfine Tuning of Donor Spins in Silicon Using Hydrostatic Strain.

We experimentally study the coupling of group V donor spins in silicon to mechanical strain, and measure strain-induced frequency shifts that are linear in strain, in contrast to the quadratic dependence predicted by the valley repopulation model (VRM), and therefore orders of magnitude greater than that predicted by the VRM for small strains |ϵ|<10^{-5}. Through both tight-binding and first principles calculations we find that these shifts arise from a linear tuning of the donor hyperfine interaction term by the hydrostatic component of strain and achieve semiquantitative agreement with the experimental values. Our results provide a framework for making quantitative predictions of donor spins in silicon nanostructures, such as those being used to develop silicon-based quantum processors and memories. The strong spin-strain coupling we measure (up to 150 GHz per strain, for Bi donors in Si) offers a method for donor spin tuning-shifting Bi donor electron spins by over a linewidth with a hydrostatic strain of order 10^{-6}-as well as opportunities for coupling to mechanical resonators.