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

提出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体（2DEG）的基本量子力学。圆偏振激光沿外加磁场方向入射时，量子阱结构中带间跃迁的光抽运导致阱中电子的自旋极化不平衡。形成阱的材料中的原子核，例如砷化镓，通过它们与电子自旋的超精细耦合而动态极化，并且它们的核磁共振信号监测阱中的电子自旋状态。研究目标是绘制(1)多粒子基态的自旋构型；(2)基态的基本激发及其能量分裂。OPNMR实验也将寻找维格纳晶体相存在的证据。这项研究将采用一种新的实验技术，“光泵浦核磁共振”（OPNMR），来研究由砷化镓等化合物半导体制成的量子阱纳米结构中二维电子气体（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光泵浦带间电子跃迁，导致井中电子自旋的非平衡极化。因此，半导体材料中的原子核通过与电子的相互作用动态极化，其核磁共振（NMR）信号用于监测阱中电子自旋的状态。研究目标是绘制出(1)井中电子集体（多粒子）最低能态的自旋构型与电子数的函数关系，以及(2)电子系统的所谓基本激发及其从最低能态产生的能量分裂。OPNMR实验还将用于寻找所谓的电子（维格纳）晶体的证据，这是一种异质结构层内二维晶格上电子的奇异组织，被认为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. ***