External seminar archive:

# Rydberg excitons in cuprous oxide - Fred Combley Colloquium

4 May 2017

Professor Manfred Bayer, TU Dortmund

Excitons determine the optical properties of semiconductors. Their description as hydrogen atom-like complexes has turned out to be an extremely successful concept.

In Rydberg atoms an electron is promoted into a state with very high principal quantum number. Thereby the atom becomes a mesoscopic quantum object with dimensions in the micrometre-range.

Recently, it was shown that also an exciton can be highly excited by observing states with principal quantum number up to n=25 in natural cuprous oxide crystals [1]. This corresponds to an average radius of more than 1µm so that the exciton wave function covers more than 10 billion crystal unit cells.

In this contribution similarities to and differences from atoms will be discussed for these Rydberg excitons. Examples are scaling laws that characterise the splitting of the exciton levels at zero [2] and at finite electric or magnetic fields like the field strengths where level resonances occur, the polarisability in electric field or the ionisation field strength.

Applying a magnetic field, a complex level splitting pattern arises that corresponds to unconventional quantum chaos for which all anti-unitary symmetries are broken [3]. Also we will discuss coherent effects at the quantum level like the Rydberg blockade or the formation dressed states [4].

Figure 1. Contour plot of absorption spectra of cuprous oxide. Below 2.170 eV energy the system behaves regularly, above it shows quantum chaotic behaviour, as evidenced by pronounced anticrossings.

## References

T. Kazimierczuk, D. Fröhlich, S. Scheel, H. Stolz and M. Bayer, Nature, 514, 343 (2014).

J. Thewes, J. Heckötter, T. Kazimierczuk, M. Aßmann, D. Fröhlich, M. Bayer, M. A. Semina and M. M. Glazov, Phys. Rev. Lett., 115, 027402 (2015).

M. Assmann, J. Thewes, D. Fröhlich and M. Bayer, Nature Materials, 15, 741 (2016).

P. Grünwald, M. Aßmann, J. Heckötter, D. Fröhlich, M. Bayer, H. Stolz and S. Scheel, Phys. Rev. Lett., 117, 133003 (2016).