The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and d=2 the time dependence of the space-integrated spin polarization, P(t), is dominated by a superexponential decay, crossing over to a stretched exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P(t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d=1 vs. d=3). Furthermore, we investigate in detail the coordinate dependence of the time-integrated spin polarization, $σ(r)$, which can be probed in the spin transport experiments with spin-polarized electrodes. We demonstrate that, while $σ(r)$ is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin decay length on the external magnetic and electric fields.
Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators
Hyperfine interactions between electron and nuclear spins have been widely used in material science, organic chemistry, and structural biology as a sensitive probe to the local chemical environment through spatial identification of nuclear spins. With the nuclear spins identified, the isotropic and anisotropic components of the hyperfine interactions in turn offer unique insight into the electronic ground-state properties of the paramagnetic centers. However, traditional ensemble measurements of hyperfine interactions average over a macroscopic number of spins with different geometrical locati…
Certain species of living creatures are known to orientate themselves in the geomagnetic field. Given the small magnitude of approximately 48 μT, the underlying quantum mechanical phenomena are expected to exhibit coherence times approaching the millisecond regime. In this contribution, we show sensitivity of organic light-emitting diodes (OLEDs) to magnetic fields far below Earth's magnetic field, suggesting that coherence times of the spins of charge-carrier pairs in these devices can be similarly long. By electron paramagnetic resonance (EPR) experiments, a lower bound for the coherence tim…
Spin Relaxation in Single Layer Graphene with Tunable Mobility
石墨烯是自旋电子学的一种有吸引力的材料，这是由于低自旋轨道和超精细耦合产生的长自旋寿命的理论预测。然而，在实验中，通过Hanle效应测量的单层石墨烯（SLG）的自旋寿命比理论上预期的要短得多。因此，SLG中自旋弛豫的起源是石墨烯自旋电子学的主要问题。尽管有大量的理论和实验工作来解决这个问题，但自旋弛豫的微观起源仍然很不清楚。通过使用有机配体结合的纳米粒子作为电荷库，调整迁移率在2700和12000 cm 2/Vs之间，我们成功地隔离了SLG中带电杂质散射对自旋弛豫的影响。我们的结果表明，虽然带电杂质可以大大影响迁移率，自旋寿命不受带电杂质散射。
Discrimination between spin-dependent charge transport and spin dependent recombination in π-conjugated polymers by correlated current and electroluminescence-detected magnetic resonance
Millisecond spin relaxation times of distinct electron and hole subensembles in MA$_x$FA$_{1-x}$PbI$_3$ perovskite crystals
Technische Universität Dortmund（多特蒙德工业大学）；Shanghai Institute of Technology（上海应用技术大学）；ETH Zürich（苏黎世联邦理工学院）；Empa-Swiss Federal Laboratories for Materials Science and Technology（瑞士联邦材料科技研究院）
