Quadrupolar Effects on Nuclear Spins of Neutral Arsenic Donors in   Silicon
  We present electrically detected electron nuclear double resonance measurements of the nuclear spins of ionized and neutral arsenic donors in strained silicon. In addition to a reduction of the hyperfine coupling, we find significant quadrupole interactions of the nuclear spin of the neutral donors of the order of 10 kHz. By comparing these to the quadrupole shifts due to crystal fields measured for the ionized donors, we identify the effect of the additional electron on the electric field gradient at the nucleus. This extra component is expected to be caused by the coupling to electric field gradients created due to changes in the electron wavefunction under strain. 
David P. Franke, Moritz P. D. Pfl\"uger, Pierre-Andr\'e Mortemousque,   Kohei M. Itoh, Martin S. Brandt
cond-mat.mtrl-sci quant-ph