Paraexcitons of Cu2O confined by a strain trap and high magnetic fields

Dynamics of excitons in a potential trap at ultra-low temperatures: paraexcitons in Cu2O

“…The typical parameters for the para-and orthoexciton traps in the experiments described in this paper are given in table 1. We also found that in order to obtain the measured potential by the Hertzian theory, we had to increase the nominal radius of the stressor lens by a factor of 1.5, which is similar to that reported in [27]. Excitons are created by a dye laser propagating normal to the strain along the x-direction.…”

“…The use of natural cuprous oxide crystals originally found in Namibia. From these crystals millimetre-sized cubic-shaped specimens with well-defined facets were prepared (see [27] for details). The quality of these samples was checked according to a low defect density, leading to long paraexciton lifetimes up to 1 µs.…”

“…The equipotential contours in the y, z-plane for paraexcitons are shown in figure 2. This potential V ex (x, y, z) can be calculated from the known strain parameters of the yellow exciton states (for a recent calculation with refined parameters, see [27]). However, comparing the low-energy border lines of the measured spatio-spectral intensities, which should closely follow the potential profile, with calculated potentials (see e.g.…”

“…In the experimental setup (figure 1), the emitted light was imaged onto the entrance slit of a high-resolution triple spectrograph (T64000, Jobin Yvon) usable in either subtractive or additive mode with a diffraction limited spatial resolution of the order of 10 µm. The astigmatism of the spectrograph was corrected by a cylindrical lens (focal length F = −1000 mm/F = 1000 mm for subtractive and additive dispersion, respectively) in front of the entrance slit [27]. For a spatially resolved spectrum I (z, ω) along the direction of the applied strain, the luminescence from a small stripe centred in the trap, with width 2 y, was integrated along the x-direction perpendicular to z (see figure 1).…”

Biexciton as a Feshbach resonance and Bose–Einstein condensation of paraexcitons in Cu2O

“…A collisional loss is believed to prevent the paraexciton density from being as high as necessary for BEC [7,[12][13][14][15][16][17][18], but an established understanding of the process is still lacking [19]. The loss rate has been found to increase with stress in strain-induced harmonic traps [16], which are needed to avoid paraexciton heating and diffusion as well as to lower the critical density [7,20,21]. Thus experiments lately have been conducted with moderate stress at subkelvin temperatures involving low critical densities [10][11][12][13].…”