Rydberg Excitons in the Presence of an Ultralow-Density Electron-Hole Plasma

Abstract

We study the Rydberg exciton absorption of Cu_{2}O in the presence of free carriers injected by above-band-gap illumination. Already at plasma densities ρ_{EH} below one hundredth electron-hole pair per μm^{3}, exciton lines are bleached, starting from the highest observed principal quantum number, while their energies remain constant. Simultaneously, the band gap decreases by correlation effects with the plasma. An exciton line loses oscillator strength when the band gap approaches its energy, vanishing completely at the crossing point. Adapting a plasma-physics description, we describe the observations by an effective Bohr radius that increases with rising plasma density, reflecting the Coulomb interaction screening by the plasma.

Interaction of Rydberg excitons in cuprous oxide with phonons and photons: optical linewidth and polariton effect

“…In a naïve picture, this process should set the limits to the observability of high quantum number states due to thermal ionization of the excitons. However, in recent work on the behavior of Rydberg excitons in the presence of an electron-hole plasma [40], no additional broadening of the absorption lines due to the electron-hole plasma has been found, which means that the process of thermal ionization should be negligible. To include in the theory an electron-hole plasma interacting with the excitons which mainly leads to a band gap shift without changing the exciton energies [40], we include a band gap shift of -D in the calculation.…”

“…However, in recent work on the behavior of Rydberg excitons in the presence of an electron-hole plasma [40], no additional broadening of the absorption lines due to the electron-hole plasma has been found, which means that the process of thermal ionization should be negligible. To include in the theory an electron-hole plasma interacting with the excitons which mainly leads to a band gap shift without changing the exciton energies [40], we include a band gap shift of -D in the calculation. Then the quantity K b (equation (2.17)) which sets the limits for the integrations over the phonon wave vectors is given by which was the maximum value of the band gap shift observed in the experiments [29] thermal ionization is only possible for n 12,13 = since all states with n 14  vanish due to the Mott effect [29].…”

Magneto-Stark and Zeeman effect as origin of second harmonic generation of excitons in Cu2O

“…II the SHG intensity is given by Eq. (19), which is plotted as function of the two polarization angles in Fig. 16(a).…”

“…[42]), in which the relative weight of the Zeeman effect and the magneto-Stark effect interfering in the SHG generation is varied, see Eq. (19). In detail, the weight of the Zeeman effect is increased from zero to unity, corresponding to its exclusive contribution.…”

Magneto-excitons in Cu2O: theoretical model from weak to high magnetic fields

“…In the calculations we used the eigenvalues n1 1 G  of the damping operator G (see (2)). Those values were estimated, for the case B=0, by fitting the experimental absorption curves by Kazimierczuk et al [1], and Hecktötter et al [22], see also [23].…”