December 2017

Abstracts of the QSIT Lunch Seminar, Thursday, December 7, 2017

Progress with Implantation Patterned Back Gates for Ultra-High Quality GaAs/AlGaAs Heterostructure Epitaxy

Matthias Berl  – Advanced semiconductor quantum materials(Wegscheider group), ETH Zurich

Gate patterning is mandatory for meso- and nanoscopic scale devices such as quantum point contacts. While patterned top gates can be realized with relative ease, the implementation of patterned back gates is very demanding. Ideally, the patterned back gate needs to be buried between substrate and heterostructure to attain sufficiently low distance between back gate and 2DEG. Moreover, the quality of the heterostructure epitaxy should not be limited by a patterned substrate.

We developed a reliable technique to implement patterned back gates for ultra-high quality 2DEGs. Our new patterned back gate technology is especially promising in the following fields:

  1. Reliable contacting of 2DES and back gate with a wide gate tuning range without risking electrical shorts.
  2. Nanoscopic gating via closely spaced 2DES and back gate (~100nm) while retaining high quality heterostructures.
  3. Extremely high quality 2DEG accessible by pushing the density limits with patterned top and back gates, reaching world record mobilities.
  4. Sophisticated gating of double layer 2DEG and/or 2DHG systems which must be tuned independently through a top and a back gate.

Parametric instabilities in a driven-dissipative BEC in a cavity

Luca Papariello – Strongly correlated electrons (Sigrist group), ETH Zurich

We study the dynamics of a BEC in a dissipative optical cavity subject to a time-periodic pump field. Beyond the unordered (normal) and self-organised (superradiant) phases, a third nonequilibrium phase emerges as a many-body parametric resonance. This dynamical normal phase switches between two symmetry-broken superradiant configurations permitted by the undriven Hamiltonian. This interacting driven-dissipative system also displays heating characteristics which depend on its phase.

JavaScript has been disabled in your browser