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

小行星9501925 该研究利用一种新的实验技术，“光泵核磁共振”，研究强磁场中二维电子气（2DEG）的基本量子力学。 在量子阱结构中，沿着外加磁场方向入射的圆偏振激光的带间跃迁的光泵浦导致阱中电子的非平衡自旋极化。 形成阱的材料中的核，例如，GaAs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NMR信号监测阱中的电子自旋状态。 研究的目标是：（1）多粒子基态的自旋组态，（2）基态的元激发及其能量分裂。 OPNMR实验也将寻找维格纳晶体相出现的证据。 这项研究将采用一种新的实验技术，“光泵核磁共振”（OPNMR），研究二维电子气（2DEG）的基本量子力学，该电子气被限制在由砷化镓等化合物半导体制成的量子阱纳米结构中。 使用沿所施加磁场的方向沿着施加的圆偏振激光的带间电子跃迁的光学泵浦导致阱中电子自旋的非平衡偏振。 因此，制造阱的半导体材料中的核通过它们与电子的相互作用而动态地极化，并且它们的核磁共振（NMR）信号用于监测阱中的电子自旋的状态。 研究目标是：（1）阱中电子的集体（多粒子）最低能态的自旋组态随电子数的变化，（2）电子系统的元激发及其从最低能态的能量分裂。 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电子到二维晶格上的奇异组织，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. ***