Department of Physics and ‡Benjamin Levich Institute, CUNY-City College of New York , New York, New York 10031, United States.
Nano Lett. 2014 May 14;14(5):2471-8. doi: 10.1021/nl500147b. Epub 2014 Apr 28.
Optical pumping of spin polarization can produce almost complete spin order but its application is restricted to select atomic gases and condensed matter systems. Here, we theoretically investigate a novel route to nuclear spin hyperpolarization in arbitrary fluids in which target molecules are exposed to polarized paramagnetic centers located near the surface of a host material. We find that adsorbed nuclear spins relax to positive or negative polarization depending on the average paramagnetic center depth and nanoscale surface topology. For the particular case of optically pumped nitrogen-vacancy centers in diamond, we calculate strong nuclear spin polarization at moderate magnetic fields provided the crystal surface is engineered with surface roughness in the few-nanometer range. The equilibrium nuclear spin temperature depends only weakly on the correlation time describing the molecular adsorption dynamics and is robust in the presence of other, unpolarized paramagnetic centers. These features could be exploited to polarize flowing liquids or gases, as we illustrate numerically for the model case of a fluid brought in contact with an optically pumped diamond nanostructure.
自旋极化的光泵浦可以产生几乎完全的自旋序，但它的应用仅限于选择的原子气体和凝聚态系统。在这里，我们理论上研究了一种在任意流体中实现核自旋超极化的新途径，其中目标分子暴露于位于主材料表面附近的极化顺磁中心。我们发现，吸附核自旋根据平均顺磁中心深度和纳米尺度表面拓扑结构弛豫到正或负极化。对于金刚石中光泵浦氮空位中心的特殊情况，我们计算了在中等磁场下的强核自旋极化，前提是晶体表面经过工程设计，具有几纳米范围内的表面粗糙度。平衡核自旋温度仅与描述分子吸附动力学的相关时间弱相关，并且在存在其他非极化顺磁中心时具有鲁棒性。这些特性可以用来极化流动的液体或气体，我们通过数值方法说明了模型情况下与光泵浦金刚石纳米结构接触的流体的情况。
