Stone Katherine W, Gundogdu Kenan, Turner Daniel B, Li Xiaoqin, Cundiff Steven T, Nelson Keith A
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
Science. 2009 May 29;324(5931):1169-73. doi: 10.1126/science.1170274.
The motions of electrons in solids may be highly correlated by strong, long-range Coulomb interactions. Correlated electron-hole pairs (excitons) are accessed spectroscopically through their allowed single-quantum transitions, but higher-order correlations that may strongly influence electronic and optical properties have been far more elusive to study. Here we report direct observation of bound exciton pairs (biexcitons) that provide incisive signatures of four-body correlations among electrons and holes in gallium arsenide (GaAs) quantum wells. Four distinct, mutually coherent, ultrashort optical pulses were used to create coherent exciton states, transform these successively into coherent biexciton states and then new radiative exciton states, and finally to read out the radiated signals, yielding biexciton binding energies through a technique closely analogous to multiple-quantum two-dimensional Fourier transform (2D FT) nuclear magnetic resonance spectroscopy. A measured variation of the biexciton dephasing rate indicated still higher-order correlations.
固体中电子的运动可能会因强的、长程的库仑相互作用而高度相关。相关的电子 - 空穴对（激子）可通过其允许的单量子跃迁进行光谱探测，但可能强烈影响电子和光学性质的高阶相关性却一直难以研究。在此，我们报告了对束缚激子对（双激子）的直接观测，这些双激子为砷化镓（GaAs）量子阱中电子和空穴之间的四体相关性提供了敏锐的特征。我们使用四个不同的、相互相干的超短光脉冲来创建相干激子态，将这些态依次转换为相干双激子态，然后再转换为新的辐射激子态，最后读出辐射信号，通过一种与多量子二维傅里叶变换（2D FT）核磁共振光谱密切类似的技术得出双激子结合能。对双激子退相速率的测量变化表明存在更高阶的相关性。
