通过突然热跳跃的无微波动态核极化
Microwave-free dynamic nuclear polarization via sudden thermal jumps
摘要：
动态核极化（DNP）目前是增强核磁共振测量灵敏度的优选策略，但其应用依赖于使用高频微波来操纵电子自旋，随着所施加的磁场的增长，这是一项越来越苛刻的任务。在这里，我们研究了一个系统的动力学托管极化剂形成的两个不同的顺磁中心附近的水平反交叉。我们从理论上表明，核自旋有效地结合交替的热跳跃和射频脉冲连接混合状态与相反的核和电子自旋对齐的循环协议。这个过程的核心是任一电子自旋物种的自旋-晶格弛豫时间之间的差异，在每次热跳跃后瞬时驱动电子自旋浴脱离平衡。在不需要微波激发的情况下，这种增强核极化的途径可以证明是方便的，特别是如果极化剂被设计成在高磁场下具有电子能级反交叉的特征。
英文摘要：
Dynamic Nuclear Polarization (DNP) presently stands as the preferred strategy to enhance the sensitivity of nuclear magnetic resonance measurements, but its application relies on the use of high-frequency microwave to manipulate electron spins, an increasingly demanding task as the applied magnetic field grows. Here we investigate the dynamics of a system hosting a polarizing agent formed by two distinct paramagnetic centers near a level anti-crossing. We theoretically show that nuclear spins polarize efficiently under a cyclic protocol that combines alternating thermal jumps and radio-frequency pulses connecting hybrid states with opposite nuclear and electronic spin alignment. Central to this process is the difference between the spin-lattice relaxation times of either electron spin species, transiently driving the electronic spin bath out of equilibrium after each thermal jump. Without the need for microwave excitation, this route to enhanced nuclear polarization may prove convenient, particularly if the polarizing agent is designed to feature electronic level anti-crossings at high magnetic fields.
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