Experimentelle Physik 2, Technische Universität Dortmund, D-44221 Dortmund, Germany.
Institut für Physik, Universität Rostock, D-18051 Rostock, Germany.
Nature. 2014 Oct 16;514(7522):343-7. doi: 10.1038/nature13832.
A highly excited atom having an electron that has moved into a level with large principal quantum number is a hydrogen-like object, termed a Rydberg atom. The giant size of Rydberg atoms leads to huge interaction effects. Monitoring these interactions has provided insights into atomic and molecular physics on the single-quantum level. Excitons--the fundamental optical excitations in semiconductors, consisting of an electron and a positively charged hole--are the condensed-matter analogues of hydrogen. Highly excited excitons with extensions similar to those of Rydberg atoms are of interest because they can be placed and moved in a crystal with high precision using microscopic energy potential landscapes. The interaction of such Rydberg excitons may allow the formation of ordered exciton phases or the sensing of elementary excitations in their surroundings on a quantum level. Here we demonstrate the existence of Rydberg excitons in the copper oxide Cu2O, with principal quantum numbers as large as n = 25. These states have giant wavefunction extensions (that is, the average distance between the electron and the hole) of more than two micrometres, compared to about a nanometre for the ground state. The strong dipole-dipole interaction between such excitons is indicated by a blockade effect in which the presence of one exciton prevents the excitation of another in its vicinity.
一个高度激发的原子，其中一个电子已经跃迁到具有较大主量子数的能级，就是类氢原子，称为里德伯原子。里德伯原子的巨大尺寸导致了巨大的相互作用效应。监测这些相互作用为原子和分子物理在单量子水平上提供了深入的了解。激子——半导体中基本的光激发，由一个电子和一个带正电荷的空穴组成——是氢的凝聚态类似物。具有类似于里德伯原子的扩展的高度激发激子很有趣，因为它们可以使用微观能量势景观以高精度放置和移动在晶体中。这种里德伯激子的相互作用可能允许形成有序激子相或在量子水平上感测其周围的基本激发。在这里，我们证明了在氧化铜 Cu2O 中存在里德伯激子，其主量子数高达 n = 25。这些状态具有巨大的波函数扩展（即，电子和空穴之间的平均距离），超过 2 微米，而基态约为 1 纳米。这种激子之间的强偶极子-偶极子相互作用表现为阻塞效应，其中一个激子的存在阻止了其附近另一个激子的激发。
