Abstracts 2017

Abstracts of the QSIT Lunch Seminar, Thursday, March 2, 2017

Ultrastrong coupling physics with metamaterials on sGe 2D hole gases: towards Dicke physics

Juanine Keller - Quantum Optoelectronics Group (Faist group), ETH Zurich,

Ultra-strong light-matter interactions can be realized in various physical systems and has thus attracted many experimental and theoretical investigations. One possible realization is to couple strongly subwavelength split ring resonators (SRR) to the Landau level transition of a two dimensional electron or hole gas. In previous work on parabolic AlGaAs/GaAs quantum wells (QWs), we showed that very high values of the normalized vacuum Rabi frequency Ω/ω = 0.87 can be reached. Strained Ge (sGe) quantum wells, which are used for the present study, are very appealing as the material exhibits a non-parabolic quantum well. In the last years, theoretical investigations about the effects of coupling to Landau level transitions with a linear band structure, as in graphene, have been debated. The frequency of the polariton branches in this case can be described by the Dicke model. For strong enough couplings (Ω/ω > ~ 0.3), the polariton frequencies start to deviate significantly from the course that is predicted for parabolic quantum wells. The strained Ge QWs provide a platform which is not linear as in graphene, but nevertheless exhibits a non-parabolicity, for which we expect the polaritons frequencies to deviate from parabolic QW measurements.

Scattering mechanisms of highest-mobility InAs/AlxGa1−xSb quantum wells

Thomas Tschirky - Advanced Semiconductor Quantum Marerials (Wescheider group), ETH Zurich

Heterostructures containing InAs have been studied due to their potential applications in high speed, low power and radiation tolerant electronics. Their narrow bandgap and strong spin-orbit coupling makes them ideal for spintronic devices research. In recent years, research on InAs quantum wells has gained significance due to their similarity to InAs/GaSb composite quantum wells for 2D topological insulators and due to new prospects for realizing a topological superconducting phase supporting Majorana fermions when combined with s-wave superconductors. In this presentation, we detail our improvements in molecular beam epitaxy growth of highest mobility InAs/AlGaSb quantum wells. The achieved electron mobility in our samples is more than double the previous record value, which held up for many years. With magnetotransport measurements on these samples, we also determine the remaining mobility limiting scattering processes and thus lay the groundwork for future improvements.