Rostock 2019 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 11: Ultra-cold plasmas and Rydberg systems

A 11.14: Poster

Dienstag, 12. März 2019, 16:30–18:30, S Fobau Physik

Optical activation of dipole-forbidden exciton transitions in cuprous oxide (Cu₂O) using orbital angular momentum light — •Annika Konzelmann and Harald Giessen — 4th Physics Institute, Center for Integrated Quantum Science and Technology IQST, and Research Center SCoPE, University of Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany

Inspired from Rydberg atoms, we investigate the semiconductor equivalent of macroscopic quantum states in cuprous oxide, which have been discovered only recently. Cu₂O has a direct bandgap of 2.17 eV and is unique due to its large Rydberg energy of 90 meV and its large effective permittivity є₁=9.8, resulting in the formation of excitons (electron-hole pairs), which are spatially extended over many thousands of lattice sites and spectroscopically well resolvable. Atomic transitions can be driven if the overlap of ground state of the crystal and excited exciton state contains the symmetry of the corresponding light excitation. We want to modify the selection rules by tuning the properties of the light, in particular, by adding angular momentum to the light. This is done by imposing a phase delay to the light beam by, e.g., using a spiral phase plate, resulting in a Laguerre-Gauss mode. We show theoretically (by symmetry considerations), that the transition selection rules can be modified, and that 1-photon-forbidden transition states become allowed states, as the spatial mode of the light is transferred to the exciton states due to phase (angular momentum) conservation.