Coherent measurements of high-order electronic correlations in quantum wells

Abstract

Strong, long-range Coulomb interactions can lead to correlated motions of multiple charged particles, which can induce important many-body effects in semiconductors. The exciton states formed from correlated electron-hole pairs have been studied extensively, but basic properties of multiple-exciton correlations-such as coherence times, population lifetimes, binding energies and the number of particles that can be correlated-are largely unknown because they are not spectroscopically accessible from the ground state. Here we present direct observations of high-order coherences in gallium arsenide quantum wells, achieved using two-dimensional multiple-quantum spectroscopy methods in which up to seven successive light fields were used. The measurements were made possible by the combination of a reconfigurable spatial beam-shaper that formed multiple beams in specified geometries and a spatiotemporal pulse-shaper that controlled the relative optical phases and temporal delays among pulses in all the beams. The results reveal triexciton coherences (correlations of three excitons or six particles), whose existence was not obvious because the third exciton spin is unpaired, and the values of their coherence times and binding energies. Rephasing of biexcitons, triexcitons and unbound two-exciton coherences was demonstrated. We also determined that there are no significant unbound correlations of three excitons and no bound or unbound four-exciton (eight-particle) correlations. Thus, the limits, as well as the properties, of many-body correlations in this system were revealed. The measurement methods open a new window into high-order many-body interactions in materials and molecules, and the present results should guide ongoing work on first-principles calculations of electronic interactions in semiconductor nanostructures.

Intervalley biexcitons and many-body effects in monolayerMoS2

“…Studying intervalley biexcitons could offer a new concept of quasiparticles in solids where valleypseudospin states play significant roles, apart from the usual atom-like orbital and spin states. The large biexciton binding energies in this material offer a promising direction to search for higher-order bound excitons such as triexcitons and the elusive quadexcitons 35,36 as well as their interplay with spin-valley degrees of freedom. We also found that, while two excitons can interact and form a biexciton, the interactions between free excitons in this system reveal a large energy red-shift that obeys a simple power-law behavior with density.…”

On the formation and decay of a molecular ultracold plasma

“…The effects of correlation are complex and difficult to study, but play an important role in shaping behaviour on a scale as large as stars and as small as quantum dots [2,3]. Ultracold plasmas offer one of the simplest possible means to approach the conditions of strong Coulomb coupling.…”

Coherent two-dimensional photocurrent spectroscopy in a PbS quantum dot photocell

“…Such effects in nanoconfined systems are readily observed using non-linear spectroscopic methods. In particular, two-dimensional electronic spectroscopy (2DES) can be used to study many-body effects in semiconductor nanoparticles, quantum wells and atomic vapours [7][8][9] .…”