Richard L. Greene Dissertation Award Talk: Probing Exotic Phases of Interacting Two-dimensional Carriers Using One-dimensional Potential Modulation

Clean two-dimensional electron systems (2DESs) subjected to a perpendicular magnetic field exhibit an array of exotic phases. At and near zero field, the 2D electrons typically form a degenerate Fermi gas and occupy a Fermi sea in their ground-state. At higher fields, however, their ground-state can transform into various phases such as the integer and fractional quantum Hall states, Fermi gas of composite fermions, stripe and bubble phases, Wigner crystal, etc. The evolution into different phases as a function of field, and in some cases temperature, makes the 2DES very exciting. Here we report our recent studies on some of these phases probed by an external, gentle periodic potential modulation. The modulation is achieved through the piezo-electric effect in GaAs as we fabricate a periodic, strain-inducing super-lattice on the surface of our samples. Using this novel technique, we have investigated: (i) the Fermi contour splitting of 2D electrons under strong in-plane magnetic fields, (ii) the spin polarization of composite fermions near the fractional quantum Hall state at filling factor 5/2, (iii) reorientation of the stripe phases at filling factor 7/2, (iv) different behavior of composite fermions near the bilayer fractional quantum Hall states at filling factors 1 and ½, (v) warped Fermi contour of composite fermions at filling factor 1/2, etc. Our results establish the periodic potential modulation as a versatile probe for the different phases of 2DESs.