CPM Seminar

Electrons in Flatlands: Surprises never stop

Mansour Shayegan

Princeton University

The high-mobility two-dimensional electron system at a GaAs/AlGaAs interface has provided the testing ground for some of the most exciting phenomena in solid state physics. Cooled to low temperatures and subjected to a perpendicular magnetic field, this system has led to the observation of new, often completely unexpected, electronic states. Examples include the fractional quantum Hall state, charge density modulated states (striped phases), charge-flux composite Fermions, and states with unusual spin-texture (Skyrmions). In this talk, I will talk about carriers in two, not so commonly studied flatlands, namely bilayer systems where holes occupy two, very closely-spaced GaAs quantum wells, and 2D electron systems confined to an AlAs quantum well where there is multi-valley degeneracy. I will show how the additional (layer and valley) degrees of freedom lead to new phenomena, some of which has no counterpart in the standard, GaAs single-layer 2D system. A highlight is the observation of electron-hole pairing in the bilayer system, and the Bose-Einstein condensation of the pairs into a superfluid state.