Ji, X., et al., Overhauser effects in non-conducting solids at 1.2 K. J. Magn. Reson., 2018. 286: p. 138-142.
Recently, it was observed that protons in non-conducting solids doped with 1,3-bisdiphenylene-2-phenylallyl (BDPA) or its sulfonated derivative (SA-BDPA) can be polarized through Overhauser effects via resonant microwave irradiation. These effects were present under magic angle spinning conditions in magnetic fields between 5 and 18.8T and at temperatures near 100K. This communication reports similar effects in static samples at 6.7T and, more importantly, at temperatures as low as 1.2K, in a different dynamic regime than in the previous study. Our results provide new information towards understanding the mechanism of the Overhauser effect in non-conducting solids. We discuss possible origins of the fluctuations that can give rise to an Overhauser effect at such low temperatures.