Giant Rydberg Excitons in Synthetic and Artificial Cuprous Oxide

Abstract

High-lying Rydberg states of Mott-Wannier excitons are receiving considerable interest due to the possibility of adding long-range interactions to the physics of exciton-polaritons. Here, we study Rydberg excitation in bulk synthetic cuprous oxide grown by the optical float zone technique and compare the result with natural samples. X-ray characterization confirms both materials are mostly single crystal, and mid-infrared transmission spectroscopy revealed little difference between synthetic and natural material. The synthetic samples show principal quantum numbers up to n = 10, exhibit additional absorption lines, plus enhanced spatial broadening and spatial inhomogeneity. Room temperature and cryogenic photoluminescence measurements reveal a significant excess of copper vacancies in the synthetic material. These measurements provide a route towards achieving high-n excitons in synthetic crystals, opening a route to scalable quantum devices.

High-resolution nanosecond spectroscopy of even-parity Rydberg excitons in Cu2O

“…10 the second location was slightly red-shifted relative to those at the first location. This confirmed our previous absorption measurements [33] that showed the crystalline environment varying slightly across the sample and giving rise to subtle but measurable changes in peak energies. However, although the amplitudes and widths of the peaks changed dramatically in the spectrum at the new location, the rapid drop to zero of the SHG signal above n = 12 was still present.…”

“…Previous experiments have also shown that the visibility of high-n excitons varies locally even in the highest quality samples, with some regions of the sample exhibiting both stronger lines and a higher maximum value of n [21]. We have previously shown [33] that our natural samples exhibit variation in the exciton spectrum on a length scale of tens of µm. Therefore, we exploited the spatial resolution of our SHG spectroscopy setup to measure the SHG spectrum and the SHG intensity at different locations across the sample.…”

“…Here the histogram was much narrower, although the width of the distribution was much broader than can be accounted for by the measured variation in the 9D line position. In our previous measurements of the spatial variation of the absorption spectrum [33], the peak energy at n = 6 in gemstone material of a similar quality varied by <10 µeV over a typical 50 µm region. The oscillator strength did not change substantially.…”

“…Rectangular samples of 2 × 3 mm were prepared by slicing the oriented material and polishing it on both sides to a thickness of 100 ± 10 µm. Full details of the preparation process are described elsewhere [33].…”

“…The apparently abrupt cut-off of the SHG spectrum has important implications for the utility of SHG and the even-parity states in quantum optics applications. The factors governing the visibility of high-n Rydberg excitons have been extensively studied in absorption experiments on the nP series [18,20,33,59], and include Rydberg blockade [1], thermally or optically excited free carriers [20,60], charged defects [6,33,61], and local strain and disorder [18,20]. Therefore to gain further insight we carried out further experiments on the power dependence and spatial variation of the SHG spectrum.…”