V15分子磁体的退相干窗口和电子-核交叉弛豫
Decoherence window and electron-nuclear cross-relaxation in the molecular magnet V 15
摘要：
本文研究了不同微波功率下，嵌入表面活性剂DODA的V_15单分子磁体（SMM）的拉比振荡。当Rabi频率Omega_R落在质子的Larmor频率w_N附近时，观察到一个强烈的阻尼峰，而振荡的阻尼时间t_R达到比在相同温度下测量的相位相干时间t_2短10倍的值。用N-自旋模型解释了实验结果，表明在旋转参考系中，t_R与退相干通过电子/核自旋交叉弛豫直接相关.结果表明，在Rabi频率w_N-sigma_e < Omega_R < w_N范围内，这种退相干伴随着能量耗散，其中sigma_e是质子在SMM上产生的平均超超精细场（频率单位）.没有耗散的较弱阻尼发生在该耗散窗口之外。简单的局域场估计表明，在SMMV_（15）中首次观察到的这种共振微波场的快速交叉弛豫，在其它含质子的SMM（如Fe_（8）和Mn_（12））中也会发生。
英文摘要：
Rabi oscillations in the V_15 Single Molecule Magnet (SMM) embedded in the surfactant DODA have been studied at different microwave powers. An intense damping peak is observed when the Rabi frequency Omega_R falls in the vicinity of the Larmor frequency of protons w_N, while the damping time t_R of oscillations reaches values 10 times shorter than the phase coherence time t_2 measured at the same temperature. The experiments are interpreted by the N-spin model showing that t_R is directly associated with the decoherence via electronic/nuclear spin cross-relaxation in the rotating reference frame. It is shown that this decoherence is accompanied with energy dissipation in the range of the Rabi frequencies w_N - sigma_e < Omega_R < w_N, where sigma_e is the mean super-hyperfine field (in frequency units) induced by protons at SMMs. Weaker damping without dissipation takes place outside this dissipation window. Simple local field estimations suggest that this rapid cross-relaxation in resonant microwave field observed for the first time in SMMV_15 should take place in other SMMs like Fe_8 and Mn_12 containing protons, too.
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