Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112, USA.
Phys Rev Lett. 2010 Jan 8;104(1):017601. doi: 10.1103/PhysRevLett.104.017601.
Organic semiconductors offer a unique environment to probe the hyperfine coupling of electronic spins to a nuclear spin bath. We explore the interaction of spins in electron-hole pairs in the presence of inhomogeneous hyperfine fields by monitoring the modulation of the current through an organic light emitting diode under coherent spin-resonant excitation. At weak driving fields, only one of the two spins in the pair precesses. As the driving field exceeds the difference in local hyperfine field experienced by electron and hole, both spins precess, leading to pronounced spin beating in the transient Rabi flopping of the current. We use this effect to measure the magnitude and spatial variation in hyperfine field on the scale of single carrier pairs, as required for evaluating models of organic magnetoresistance, improving organic spintronics devices, and illuminating spin decoherence mechanisms.
有机半导体为探测电子自旋与原子核自旋池的超精细耦合提供了独特的环境。我们通过在相干自旋共振激发下监测有机发光二极管中的电流调制来研究电子-空穴对中自旋的相互作用，存在非均匀超精细场。在弱驱动场中，电子对中的两个自旋只有一个进动。当驱动场超过电子和空穴所经历的局部超精细场的差异时，两个自旋都会进动，导致电流的瞬态拉比翻转中的自旋拍频明显。我们利用这一效应来测量超精细场的大小和空间变化，其范围为单个载流子对，这是评估有机磁电阻模型、改进有机自旋电子器件以及阐明自旋退相干机制所必需的。
