Rydberg excitons in Cu$_2$O at millikelvin temperatures

TL;DR

This study explores the behavior of Rydberg excitons in Cu$_2$O at millikelvin temperatures, revealing their sensitivity to excitation power and the influence of internal electric fields on exciton states.

Contribution

It extends the experimental investigation of Rydberg excitons in Cu$_2$O by varying temperature and excitation power, highlighting the effects of internal electric fields on exciton behavior.

Findings

P excitons are more sensitive to excitation power than D excitons.

Internal electric fields from charged impurities affect exciton states.

Excitons with n=29 are observable at very low laser intensities.

Abstract

Rydberg excitons in the semiconductor Cu$_2$O have been observed in absorption experiments up to a principal quantum number of n = 28 at millikelvin temperatures [1]. Here, we extend the experimental parameter space by variing both temperature and excitation power. In particular, we show that the P excitons close to the band gap react more sensitively to an increase of the excitation power than states of the associated D exciton multiplet, even though the latter are located at comparatively higher energy. This finding is similar to the one observed when applying an external electric field, suggesting that the observed behavior arises from internal electric fields created by charged impurities that are optically ionized. At laser intensities below 1 $\mu$W/cm$^2$, absorption lines of excitons with n=29 are observed.