AI 中文总结
本研究通过共振二次谐波生成实验与半经典理论，探究氧化亚铜里德伯激子的相互作用，发现其与原子的范德瓦尔斯相互作用存在根本差异。
AI 中文摘要
我们利用二次谐波生成（SHG）对氧化亚铜（Cu₂O）中主量子数高达[此处原文缺失具体数值，按原文保留]的黄色系列相互作用激子开展了实验与理论研究。采用峰值强度达10 GW/cm²的皮秒脉冲激光激发，我们观测到随泵浦激光强度增加，光谱出现显著变化：向更低绝对能量方向的能量移动以及光谱展宽。低功率下，光谱线的绝对强度与泵浦功率的平方成正比，但在高功率下达到饱和；功率进一步升高时，SHG强度反而降低。为定量解释这些结果，我们建立了共振SHG的半经典理论，其中SHG过程完全相干，假设激子为玻色子，通过与距离相关的势能相互作用，既导致光谱线形变化，又通过里德伯阻塞产生饱和效应。同时开展的双光子吸收测量可推导激子-激子相互作用的定量值。尽管结果与最先进的类原子范德瓦尔斯相互作用理论计算的量级一致，但与主量子数的标度关系存在显著差异。由于三光子吸收到蓝色和紫色带态所产生的电子-空穴等离子体的可能屏蔽效应可被排除，我们的结果表明激子与原子之间存在根本差异。
英文摘要
We report experimental and theoretical investigations of interacting excitons of the yellow series in cuprous oxide (Cu$_2$O) with principal quantum numbers up to by means of second harmonic generation (SHG). Using picosecond pulsed laser excitation up to 10 GW/cm$^2$ peak intensity we observe a pronounced change of the spectra with increasing pump laser intensity: an energetic shift to lower absolute energies and a spectral broadening. The absolute intensities of the spectral lines scale for low powers with the square of the pump power, but saturates at higher powers. At still higher powers the SHG intensity is actually reduced. To explain these results quantitively, we developed a semi-classical theory of resonant SHG where the process of SHG is fully coherent. The excitons are assumed to be bosons interacting by a distance dependent potential giving rise to both the changes in spectral line shape and the saturation by a $\it{Rydberg}$ blockade. The concomitant measurement of two-photon absorption allows to derive quantitative values for the exciton-exciton interaction. While the results agree in order of magnitude with those calculated by state-of-the art atomic-like van der Waals interaction theory, the scaling with principle quantum number is quite different. As a possible screening by an electron-hole plasma created by three-photon absorption into blue and violet band states could be ruled out, our results point toward fundamental differences between excitons and atoms.
