Midinfrared properties of cuprous oxide: High-order lattice vibrations and intraexcitonic transitions of the1sparaexciton

Abstract

This contribution addresses both the general mid-infrared ͑MIR͒ properties of Cu 2 O and induced absorption due to intraexcitonic 1s → 2p transitions under simultaneous cw laser excitation. After an overview of the current state of knowledge and remaining open questions concerning excitons in Cu 2 O we will first discuss several absorption bands in the spectral range between approximately 100 and 150 meV in terms of multiphonon and biphonon features. The second, more extensive part will concern a pump-probe experiment in the limit of low densities of 1s excitons where we investigated intraexcitonic transitions appearing in the MIR spectral range as well. We find a signal which can be clearly assigned to a 1s para→ 2p para transition and present various data depending on excitation conditions and sample temperature. Applying the results of detailed theoretical considerations we can estimate the density and lifetime of the 1s para-exciton and at least speculate about its dispersion.

Transient terahertz spectroscopy of excitons and unbound carriers in quasi-two-dimensional electron-hole gases

“…While initial studies were scarce, intra-excitonic spectroscopy recently emerged as a powerful tool to investigate the low-energy resonances and dynamics of excitons, 10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28 fueled in part by rapid advances in ultrafast THz technology. 29 Optical-pump THz-probe experiments are of particular interest, as they yield both real and imaginary parts of the transient response functions.…”

Exciton dynamics in cuprous oxide

“…Cuprous oxide (Cu 2 O) is a favorable candidate for Bose-Einstein condensation, by virtue of the extraordinary long lifetime of excitons in this material which should allow for an efficient cooling of the exciton gas towards the lattice temperature, and helps to reach a sufficiently high ρ required for BEC formation. As it was reported in previous works [1][2][3], there is a possibility to probe the population of 1s paraexcitons via laser induced changes in the absorption in the infrared region due to the presence of excitons (Fig. 1).…”

Two‐photon coherent control of dark orthoexcitons in Cu2O

“…Their atomic-like sharp resonances, 1s excitons in particular, have allowed many important spectroscopic studies such as forbidden resonant Raman scattering [1], coherent polariton propagation [2], exciton Lyman spectroscopy [3][4][5], and stimulated emission in THz region [6]. The four 1s excitons are split into threefold degenerate orthoexcitons and paraexcitons by 12 meV due to the electronhole exchange interaction.…”