动态核极化热混合模型中的电子和核自旋动力学
Electron and nuclear spin dynamics in the thermal mixing model of dynamic nuclear polarization
摘要：
本文提出了一种新的计算低温热混合区动态核极化过程时间演化的数学方法。不假设任何先验的分析形式的电子极化，我们的方法提供了一个定量的图片的稳定状态，恢复众所周知的Borghini预测的基础上的热力学参数，只要电子-核的过渡速率是快的相比，其他相关的时间尺度。实质上不同的最终极化水平，而不是当后者的假设是放松的核泄漏项的存在下，即使非常弱，这表明一个可能的解释之间的偏差测量的稳态极化和Borghini预测。所提出的方法还允许计算核极化和弛豫时间，一旦指定的电子/核浓度比和涉及两个自旋物种的微观过程的典型速率。数值结果表明，占典型的DNP样品的多种动力学行为。
英文摘要：
A novel mathematical treatment is proposed for computing the time evolution of dynamic nuclear polarization processes in the low temperature thermal mixing regime. Without assuming any a priori analytical form for the electron polarization, our approach provides a quantitative picture of the steady state that recovers the well known Borghini prediction based on thermodynamics arguments, as long as the electrons-nuclei transition rates are fast compared to the other relevant time scales. Substantially different final polarization levels are achieved instead when the latter assumption is relaxed in the presence of a nuclear leakage term, even though very weak, suggesting a possible explanation for the deviation between the measured steady state polarizations and the Borghini prediction. The proposed methodology also allows to calculate nuclear polarization and relaxation times, once specified the electrons/nuclei concentration ratio and the typical rates of the microscopic processes involving the two spin species. Numerical results are shown to account for the manifold dynamical behaviours of typical DNP samples.
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