Kazmierczak Nathanael P, Oyala Paul H, Hadt Ryan G
Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States.
ACS Cent Sci. 2024 Dec 11;10(12):2353-2362. doi: 10.1021/acscentsci.4c01177. eCollection 2024 Dec 25.
Spin-lattice relaxation constitutes a key challenge for the development of quantum technologies, as it destroys superpositions in molecular quantum bits (qubits) and magnetic memory in single molecule magnets (SMMs). Gaining mechanistic insight into the spin relaxation process has proven challenging owing to a lack of spectroscopic observables and contradictions among theoretical models. Here, we use pulse electron paramagnetic resonance (EPR) to profile changes in spin relaxation rates ( ) as a function of both temperature and magnetic field orientation, forming a two-dimensional data matrix. For randomly oriented powder samples, spin relaxation anisotropy changes dramatically with temperature, delineating multiple regimes of relaxation processes for each Cu(II) molecule studied. We show that traditional fitting approaches cannot reliably extract this information. Single-crystal anisotropy experiments reveal a surprising change in spin relaxation symmetry between these two regimes. We interpret this switch through the concept of a spin relaxation tensor, enabling discrimination between delocalized lattice phonons and localized molecular vibrations in the two relaxation regimes. Variable-temperature anisotropy thus provides a unique spectroscopic method to interrogate the character of nuclear motions causing spin relaxation and the loss of quantum information.
自旋 - 晶格弛豫是量子技术发展面临的关键挑战，因为它会破坏分子量子比特（qubit）中的叠加态以及单分子磁体（SMM）中的磁记忆。由于缺乏光谱可观测量以及理论模型之间存在矛盾，深入了解自旋弛豫过程的机理颇具挑战性。在此，我们使用脉冲电子顺磁共振（EPR）来描绘自旋弛豫速率（ ）随温度和磁场取向的变化，形成一个二维数据矩阵。对于随机取向的粉末样品，自旋弛豫各向异性随温度急剧变化，为所研究的每个Cu(II)分子描绘出多个弛豫过程的区域。我们表明，传统的 拟合方法无法可靠地提取此信息。单晶 各向异性实验揭示了这两个区域之间自旋弛豫对称性的惊人变化。我们通过自旋弛豫张量的概念来解释这种转变，从而能够区分两个弛豫区域中的离域晶格声子和局域分子振动。因此，变温 各向异性提供了一种独特的光谱方法，用于探究导致自旋弛豫和量子信息丢失的核运动特性。
