标题： 周期性和非周期性π脉冲序列下二极固体中的长寿命选择性自旋回波 显示英文标题

标题： Long-lived selective spin echoes in dipolar solids under periodic and aperiodic pi-pulse trains

摘要： Carr-Purcell-Meiboom-Gill (CPMG) $\pi-$脉冲序列在动态解耦系统与其环境方面的应用已在各种物理系统中得到广泛研究。 当应用于偶极固体时，最近的实验表明，CPMG脉冲序列可以产生长寿命的自旋回波。 尽管关于CPMG序列下这些长寿命自旋回波的起源仍存在一些争议，但普遍认为在 $\pi-$脉冲期间的脉冲误差是必要的条件。 在本工作中，我们提出一种理论来描述在CPMG($\phi_{1},\phi_{2}$)脉冲序列下偶极耦合的自旋-1/2系统的自旋动力学，其中 $\phi_{1}$ 和 $\phi_{2}$是 $\pi-$脉冲的相位。 从我们的理论框架来看，CPMG($\phi_{1},\phi_{2}$)脉冲序列的传播子等价于一个有效的“脉冲”自旋锁定，其相位为$\pm\frac{\phi_{2}-3\phi_{1}}{2}$，这会产生一个周期性的准平衡状态，对应于长寿命的回波。 数值模拟以及在磁稀释的、随机自旋网络中的实验，包括C$_{60}$和C$_{70}$以及在非稀释自旋系统中的实验，包括金刚烷和二茂铁，均被进行并证实了所提出理论的预测。 显示英文摘要

摘要： The application of Carr-Purcell-Meiboom-Gill (CPMG) $\pi-$trains for dynamically decoupling a system from its environment has been extensively studied in a variety of physical systems. When applied to dipolar solids, recent experiments have demonstrated that CPMG pulse trains can generate long-lived spin echoes. While there still remains some controversy as to the origins of these long-lived spin echoes under the CPMG sequence, there is a general agreement that pulse errors during the $\pi-$pulses are a necessary requirement. In this work, we develop a theory to describe the spin dynamics in dipolar coupled spin-1/2 system under a CPMG($\phi_{1},\phi_{2}$) pulse train, where $\phi_{1}$ and $\phi_{2}$ are the phases of the $\pi-$pulses. From our theoretical framework, the propagator for the CPMG($\phi_{1},\phi_{2}$) pulse train is equivalent to an effective ``pulsed'' spin-locking of single-quantum coherences with phase $\pm\frac{\phi_{2}-3\phi_{1}}{2}$, which generates a periodic quasiequilibrium that corresponds to the long-lived echoes. Numerical simulations, along with experiments on both magnetically dilute, random spin networks found in C$_{60}$ and C$_{70}$ and in non-dilute spin systems found in adamantane and ferrocene, were performed and confirm the predictions from the proposed theory.