Tycko R, Barrett S E, Dabbagh G, Pfeiffer L N, West K W
AT&T Bell Laboratories, Murray Hill, NJ 07974, USA.
Science. 1995 Jun 9;268(5216):1460-3. doi: 10.1126/science.7539550.
An optical pumping technique was used to enhance and localize nuclear magnetic resonance (NMR) signals from an n-doped GaAs/Al0.1Ga0.9As multiple quantum well structure, permitting direct radio-frequency measurements of gallium-71 NMR spectra and nuclear spin-lattice relaxation rates (1/T1) as functions of temperature (1.6 K < T < 4.2 K) and the Landau level filling factor (0.66 < v < 1.76). The measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells. Minima in 1/T1 at v approximately 1 and v approximately 2/3 indicate energy gaps for electronic excitations in both integer and fractional quantum Hall states. Rapid, temperature-independent relaxation at intermediate v values indicates a manifold of low-lying electronic states with mixed spin polarizations.
采用光泵浦技术增强并定位了来自n型掺杂的GaAs/Al0.1Ga0.9As多量子阱结构的核磁共振（NMR）信号，从而能够直接进行射频测量镓71的NMR谱以及作为温度（1.6 K < T < 4.2 K）和朗道能级填充因子（0.66 < v < 1.76）函数的核自旋 - 晶格弛豫率（1/T1）。这些测量揭示了电子 - 电子相互作用对限制在GaAs阱中的二维电子系统的能级和自旋态的影响。在v约为1和v约为2/3时1/T1的最小值表明在整数和分数量子霍尔态中电子激发的能隙。在中间v值处快速的、与温度无关的弛豫表明存在具有混合自旋极化的多个低能电子态。
