Giant Rydberg excitons in Cu$_{2}$O probed by photoluminescence excitation spectroscopy

Abstract

Rydberg excitons are, with their ultrastrong mutual interactions, giant optical nonlinearities, and very high sensitivity to external fields, promising for applications in quantum sensing and nonlinear optics at the single-photon level. To design quantum applications it is necessary to know how Rydberg excitons and other excited states relax to lower-lying exciton states. Here, we present photoluminescence excitation spectroscopy as a method to probe transition probabilities from various excitonic states in cuprous oxide, and we show giant Rydberg excitons at T = 38 mK with principal quantum numbers up to n = 30, corresponding to a calculated diameter of 3 µm.

High resolution nanosecond spectroscopy of even-parity Rydberg excitons in Cu$_{2}$O

“…These fits yielded E g = 2.1720780 eV ± 0.4 µeV and R y = 82.40 ± 0.05 meV, and the corresponding δ L are listed in Table I. The values for the bandgap energy and Rydberg constant agree well with those obtained from recent studies of the P odd-parity excitons [1,18].…”

“…Regarding the observation of higher principal quantum number, it appears challenging to use SHG to match the n > 25 observed in absorption spectroscopy of the oddparity excitons [1,18]. Nevertheless, our results show there is clear scope for improvement.…”

“…Because both bands are of even-parity, excitons with an odd-parity Ptype envelope are dipole allowed [17]. The seminal study by Kazimierczuk et al [1] resolved excitons up to principal quantum number n = 25 and more recently Versteegh et al [18] measured up to n = 30. At these highest observed states, the spatial extent of the excitons is greater than 1 µm and the associated dipole moment is large enough to exhibit evidence of a Rydberg blockade [1,[19][20][21] arising from the van der Waals interactions between the excitons.…”

“…These properties were essential to a recent demonstration of the microwave modulation of an optical carrier in cuprous oxide [26]. It is therefore an important question whether the even-parity spectrum may be resolved up to the same high principal quantum numbers (n > 25) observed in one-photon excitation of the nP series [1,18].…”

“…The apparently abrupt cut-off of the SHG spectrum from of the even parity states 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 [18,20,32,58], and include Rydberg blockade [1], thermally or optically excited free carriers [20,59], charged defects [32,60,61], 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.…”