CAREER: Optically-Pumped Nuclear Magnetic Resonance Study of Two-Dimensional Electron Systems in Strong Magnetic Fields

9501925 Barrett建议的研究利用一种新的实验技术--光泵核磁共振，来研究强磁场中二维电子气(2DEG)的基本量子力学。在沿外加磁场方向入射的圆偏振激光作用下，量子井结构中带间跃迁的光泵浦导致了势垒中电子的非平衡自旋极化。形成势垒的材料中的原子核，如砷化镓，通过它们与电子自旋的超精细耦合而被动态极化，它们的核磁共振信号监测势垒中的电子自旋状态。研究的目标是绘制(1)多粒子基态的自旋组态，(2)基态的基元激发及其能量分裂。OP核磁共振实验还将寻找维格纳晶相存在的证据。这项拟议的研究将使用一种新的实验技术--光泵核磁共振(OP核磁共振)，来研究限制在由化合物半导体如砷化镓制成的量子阱纳米结构中的二维电子气(2DEG)的基本量子力学。利用沿外加磁场方向施加的圆偏振激光对带间电子跃迁进行光泵浦，会导致势垒中电子自旋的非平衡极化。因此，制造该井的半导体材料中的原子核通过与电子的相互作用被动态极化，并且它们的核磁共振(核磁共振)信号用于监测该井中电子自旋的状态。研究的目的是绘制(1)电子的集体(多粒子)最低能态的自旋组态以及与电子数目的函数，以及(2)电子系统的所谓基本激发态及其从最低能态的能量分裂。OP核磁共振实验还将被用来寻找所谓的电子(Wigner)晶体的证据，Wigner晶体是一种在异质结构层内的二维晶格上的奇异电子组织，据信在某些实验条件下存在。***

9501925 Barrett The proposed research utilizes a new experimental technique, "Optically Pumped Nuclear Magnetic Resonance", to study the fundamental quantum mechanics of the two-dimensional electron gas (2DEG) in strong magnetic fields. Optical pumping of interband transitions in a quantum-well structure with circularly-polarized laser light incident along the applied magnetic field direction results in non-equilibrium spin polarization of electrons in the well. Nuclei in the materials that form the well, e.g., GaAs, are dynamically polarized via their hyperfine coupling to the electron spins, and their NMR signals monitor the electron spin state in the well. The research objectives are to map out (1) the spin configuration of the many-particle ground state, and (2) the elementary excitations and their energy splitting from the ground state. OPNMR experiments will also search for evidence of occurrence of the Wigner crystal phase. %%% The proposed research will employ a new experimental technique, "Optically Pumped Nuclear Magnetic Resonance" (OPNMR), to study the fundamental quantum mechanics of the two-dimensional electron gas (2DEG) confined in quantum-well nanostructures fabricated from compound semiconductors such as gallium arsenide. Optical pumping of interband electronic transitions using circularly- polarized laser light applied along the direction of an applied magnetic field results in non-equilibrium polarization of the spins of electrons in the well. Nuclei in the semiconductor material from which the well is fabricated are consequently dynamically polarized through their interactions with the electrons, and their nuclear magnetic resonance (NMR) signals serve to monitor the state of the electron spins in the well. The research objectives are to map out (1) the spin configuration of the collective (many-particle) lowest energy state of the electrons in the well as a function of the number of electrons, and (2) the so-called elementary excita tions of the electronic system and their energy splittings from the lowest energy state. OPNMR experiments will also be used to search for evidence of the so-called electron (Wigner) crystal, an exotic organization of electrons onto a two-dimensional lattice within a heterostructure layer, which is believed to exist under certain experimental conditions. ***