Giant Rydberg excitons in the copper oxide Cu2O

Abstract

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.

Excitonic giant-dipole potentials in cuprous oxide

“…As the interaction between the two species can be modeled as a screened Coulomb interaction, excitons are often considered to be a solid-state quasi-particle analogue to the hydrogen atom [3][4][5]. In particular, excitons in cuprous oxide (Cu 2 O) have attracted quite some attention in recent years due to an outstanding experiment, in which the hydrogen-like absorption spectrum of these quasiparticles could be observed up to principal quantum numbers n = 25 [6].…”

A historic experiment redesigned

“…The giant diamagnetism in copper oxide was first observed by Gross and colleagues 7 and has been confirmed in the present experiments. Another phenomenon is Rydberg blockade, which has now been observed by Kazimierczuk and co-workers 5 and manifests as a saturation of the increase of the amplitudes of the absorption lines that correspond to large n. The violet colour shows energies of the interband optical absorption. The spectrum darkens at these energies.…”

Exponentially Correlated Gaussians for Simulating Of Localized and Autolocalized States in Polar Media

“…Несмотря на видимость относительной простоты и завершенности исследований энергетического спектра молекулы водорода, нахождение наиболее точных значений энергетических уровней этой простейшей молекулярной системы и в настоящее время представляет собой актуальную задачу как для теоретических расчетов [15][16][17], так для экспериментальных исследований. Особый интерес представляют водородоподобные ионы и ридберговы состояния атомов [18][19][20], а также их комплексы, к изучению которых можно применять методы, развитые ранее для простейших атомных и молекулярных аналогов.…”

“…Отдельного упоминания заслуживает изучение экситонов и биэкситонов. Водородоподобный спектр экситона большого радиуса в кристаллах Cu 2 O удается наблюдать вплоть до главного квантового числа n = 25 [20].…”