Nodar Samkharadze

Observation of a transition from a topologically ordered to a spontaneously broken symmetry phase

Hydrostatic pressure is used as a means to tune the two-dimensional electron gas hosted in a GaAs/AlGaAs crystal from a topologically ordered to a spontaneously broken symmetry phase.

Quantitative analysis of the disorder broadening and the intrinsic gap for the

We report a reliable method to estimate the disorder broadening parameter from the scaling of the gaps of the even and major odd denominator fractional quantum Hall states of the second Landau level. We apply this technique to several samples of vastly different densities and grown in different molecular beam epitaxy chambers. Excellent agreement is found between the estimated intrinsic and numerically obtained energy gaps for the ν = 5/2 fractional quantum Hall state. Furthermore, we quantify the dependence of the intrinsic gap at ν = 5/2 on Landau-level mixing.

\nu

We fabricated a He-3 immersion cell for transport measurements of semiconductor nanostructures at ultra low temperatures and in strong magnetic fields. We have a new scheme of field-independent thermometry based on quartz tuning fork Helium-3 viscometry which monitors the local temperature of the samples environment in real time. The operation and measurement circuitry of the quartz viscometer is described in detail. We provide evidence that the temperature of two-dimensional electron gas confined to a GaAs quantum well follows the temperature of the quartz viscometer down to 4 mK.

=5/2 fractional quantum Hall state

The region of filling factors

Integrated electronic transport and thermometry at milliKelvin temperatures and in strong magnetic fields

1/3<\nu<2/5

Observation of incompressibility at ν = 4 / 11 and ν = 5 / 13

is predicted to support new types of fractional quantum Hall states with topological order different from that of the Laughlin-Jain or the Moore-Read states. Incompressibility is a necessary condition for the formation of such novel topological states. We find that at 6.9~mK incompressibility develops only at

Onset of quantum criticality in the topological-to-nematic transition in a two-dimensional electron gas at filling factor ν=5/2

\nu=4/11

Particle-hole asymmetry of fractional quantum Hall states in the second Landau level of a two-dimensional hole system

and

Observation of Incompressibility at

5/13

\nu=4/11

, while the states at