Phonon-assisted absorption of excitons in Cu2O

Abstract

The basic theoretical foundation for the modelling of phonon-assisted absorption spectra in direct bandgap semiconductors, introduced by Elliott 60 years ago 1 using second order perturbation theory, results in a square root shaped dependency close to the absorption edge. A careful analysis of the experiments 2 reveals that for the yellow S excitons in Cu2O the lineshape does not follow that square root dependence. The reexamination of the theory shows that the basic assumptions of constant matrix elements and constant energy denominators is invalid for semiconductors with dominant exciton effects like Cu2O, where the phonon-assisted absorption proceeds via intermediate exciton states. The overlap between these and the final exciton states strongly determines the dependence of the absorption on the photon energy. To describe the experimental observed line shape of the indirect absorption of the yellow S exciton states we find it necessary to assume a momentum dependent deformation potential for the optical phonons.

Microwave-optical coupling via Rydberg excitons in cuprous oxide

“…The second harmonic is coherently generated with an emission spectrum determined by the excitation laser, and is easily separated from the excitation light. In addition, the second harmonic generation spectrum does not exhibit the large phonon-assisted background observed in onephoton transmission spectroscopy [29,64,65]. Together these advantages enable us to observe the modulation of an optical carrier by the microwave field.…”

“…1(d). In this energy range, the absorption is dominated by the background associated with phonon-assisted transitions involving the lowest-lying 1S exciton [64,65], with superimposed resonances associated with nP excitonic states. Our data shows excitons from n = 5 to n = 11, with the observation of higher n states limited by the spectral resolution of the monochromator.…”

“…Rydberg atoms show promise due to the large electric * Correspondence email address: m.p.a.jones@durham.ac.uk dipole moment associated with transitions between Rydberg states of opposite parity, which scales with principal quantum number, n, as n 2 . However compatibility between the laser cooling technology required for Rydberg atoms and the millikelvin dilution refrigerator environment of superconducting qubits is an ongoing challenge [20][21][22][23]. An alternative Rydberg platform which is more compatible with other solid state devices is offered by excitonic states in semiconductors.…”

Semiconductor Rydberg Physics

“…For Cu 2 O, the most relevant phonon is the optical ‐phonon at an energy of 13.6 meV. [ 27,28 ] Phonon‐assisted transitions to the 1S excitons of the green and yellow series are possible and form a continuous background on which the series of Rydberg exciton states resides. A typical full spectrum of Rydberg resonances including the most important contributions to the phonon background is shown in Figure 3.…”

Multicomponent exciton gas in cuprous oxide: cooling behaviour and the role of Auger decay

“…The remaining sums are solved numerically. The transition matrix element as well as the momentum dependent deformation potential are known from fits of the Γ − 3 phonon assisted absorption band edge [32]. The resulting Auger coefficient is…”