Direct observation of hyperpolarization breaking through the spin diffusion barrier

Publication of CRMN in Science Advances on April 30, 2021. Communication from the UCBL on May 19, 2021. CRMN researchers have developed a novel and simple method to better understand the fundamental magnetic properties of matter. Dynamic nuclear polarization (DNP) is a widely used tool for overcoming the low intrinsic sensitivity of nuclear magnetic resonance spectroscopy and imaging. Its practical applicability is typically bounded, however, by the so-called "spin diffusion barrier," which relates to the poor efficiency of polarization transfer from highly polarized nuclei close to paramagnetic centers to bulk nuclei. A quantitative assessment of this barrier has been hindered so far by the lack of general methods for studying nuclear polarization flow in the vicinity of paramagnetic centers. Here, we fill this gap and introduce a general set of experiments based on microwave gating that are readily implemented.