Unexpectedly slow two particle decay of ultra-dense excitons in cuprous oxide

Abstract

For an ultra-dense exciton gas in cuprous oxide (Cu 2 O), exciton-exciton interactions are the dominant cause of exciton decay. This study demonstrates that the accepted Auger recombination model overestimates the exciton decay rate following intense two photon excitation. Two exciton decay is relevant to the search for collective quantum behavior of excitons in bulk systems. These results suggest the existence of a new high density regime of exciton behavior.

Photoionization cross section of1sorthoexcitons in cuprous oxide

“…8). If the ionization pulse arrived after the pump pulse, the apparent photoionization cross section decreased rapidly owing to dispersion [13] (and the resulting spread in exciton group velocities) and Auger decay [2,6,8] of the exciton polaritons. A density dependence indicating Auger decay was demonstrated previously under similar conditions [11].…”

“…A cuprous oxide yellow 1s orthoexciton is an excellent quantum system for studies of photoionization since: 1) it shares a Rydberg-like structure with hydrogen [3] and positronium [4]; 2) it is relatively stable to radiative decay [5]; 3) there is extensive interest in strongly interacting conditions [6][7][8][9][10]; 4) nonlinear optical methods can be used to prepare the excitons [1,11,12]; and 5) the polariton (a mixed exciton/photon) state can be studied selectively [13]. Exciton photoionization was inferred from photoconductivity in the organic semiconductors anthracene [14,15], tetracene [16], and p-terphenyl [17], although the electronic structures of these materials differ significantly from that of cuprous oxide.…”

“…The process was masked, however, by: 1) third harmonic * prb@laszlofrazer.com generation [1,18], 2) Auger exciton-exciton annihilation [6], and 3) identical pump and probe photons.…”