Interactions of Rydberg excitons with charged impurities

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We investigate the interaction between Rydbergexcitons and charged impurities in the semiconductor Cu2O. In Cu2O, Rydbergexcitons with principal quantum numbers up to n=30 and extensions in the micrometer range can be observed. In analogy to Rydbergatoms, Rydbergexcitons exhibit an enormous polarizability, which renders it possible to control their state by the application of small electric fields. In this context, we expect the crystalline environment in which Rydbergexcitons are created to have a significant impact on the properties of the Rydbergstates. The presence of static electric charges leads to an electric field inducing a Stark-splitting of energy levels and mixing of states or even dissociation of energetically high states close to the band gap. The aim of the proposal at hand is to investigate and to control this detrimental impact of the impurities on the Rydberg spectrum. We will employ two-color pump-probe spectroscopy to systematically excite Rydbergexcitons with high principal quantum numbers that neutralize the electric fields of charged impurities. This may happen due to the formation of a bound exciton complex or due to the recombination of an exciton at the impurity. To investigate the microscopic mechanism of this neutralization, we plan to measure the optical response of the probed spectrum to a low-power pump beam in the steady-state as well as time-resolved. At low powers, an increase of oscillatorstrength of the probed state is expected. From the scaling of the optical response with the principal quantum number of the probed state we will be able to determine the blockade volume around an impurity, within which the excitation of excitons is blocked. The scaling with the principal quantum number of the pumped state renders it possible to determine the exact mechanism behind the interaction. Using time-resolved excitation and detection we will be able to measure the time scales of the neutralization as well as the reionization of the impurities. A deepened understanding of the interaction between Rydbergexcitons and charged impurities is of fundamental relevance to observe Rydbergexcitons with higher principal quantum numbers and Fourier-limited linewidths in Cu2O, but also other material systems, such as TMDCs.