Origin of enhanced dynamic nuclear polarization and all-optical nuclear magnetic resonance in GaAs quantum wells
Origin of enhanced dynamic nuclear polarization and all-optical nuclear magnetic resonance in GaAs quantum wells
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DOI：
10.1103/physrevb.64.195304
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发表时间：
2001-04
影响因子：
3.7
通讯作者：
G. Salis;D. Awschalom;Y. Ohno;H. Ohno
中科院分区：
文献类型：
--
作者：
G. Salis;D. Awschalom;Y. Ohno;H. Ohno
(110) GaAs 量子阱中电子自旋动力学的时间分辨光学测量用于研究强各向异性电子 g 张量的后果，以及先前发现的全光核磁共振的起源。测量了 g 张量的所有分量，发现即使沿面内方向也具有很强的各向异性。自旋信号的幅度允许研究注入自旋及其进动轴的空间方向。在电子自旋几乎横向于所施加的磁场注入的几何结构中，令人惊讶地有效的动态核极化归因于增强的非进动电子自旋分量。电子 g 因子的小绝对值与有效的核自旋极化相结合，导致在低温下主导电子自旋进动的大核场。这些效应允许灵敏地检测由周期性激发的量子阱电子引起的全光核磁共振。研究了先前观察到的 $\ensuremath{\Delta}m=2$ 跃迁的机制，发现其可归因于电四极耦合，而 $\ensuremath{\Delta}m=1$ 跃迁显示出四极和电子自旋感应磁偶极耦合的特征。
Time-resolved optical measurements of electron-spin dynamics in a (110) GaAs quantum well are used to study the consequences of a strongly anisotropic electron g tensor, and the origin of previously discovered all-optical nuclear magnetic resonance. All components of the g tensor are measured, and a strong anisotropy even along the in-plane directions is found. The amplitudes of the spin signal allow the study of the spatial directions of the injected spin and its precession axis. Surprisingly efficient dynamic nuclear polarization in a geometry where the electron spins are injected almost transverse to the applied magnetic field is attributed to an enhanced nonprecessing electron spin component. The small absolute value of the electron g factor combined with efficient nuclear spin polarization leads to large nuclear fields that dominate electron spin precession at low temperatures. These effects allow for sensitive detection of all-optical nuclear magnetic resonance induced by periodically excited quantum-well electrons. The mechanism of previously observed $\ensuremath{\Delta}m=2$ transitions is investigated and found to be attributable to electric quadrupole coupling, whereas $\ensuremath{\Delta}m=1$ transitions show signatures of both quadrupole and electron-spin induced magnetic dipole coupling.