Sukret Hasdemir

Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing

The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D) charged particles at high magnetic fields, is one of the most fascinating, macroscopic manifestations of a many-body state stabilized by the strong Coulomb interaction. It occurs when the filling factor (

Fractional quantum Hall effect and Wigner crystal of interacting composite fermions.

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Evidence for a ν = 5 / 2 fractional quantum Hall nematic state in parallel magnetic fields

) of the quantized Landau levels (LLs) is a fraction which, with very few exceptions, has an odd denominator. In 2D systems with additional degrees of freedom it is possible to cause a crossing of the LLs at the Fermi level. At and near these crossings, the FQHE states are often weakened or destroyed. Here we report the observation of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility GaAs 2D

Anisotropic composite fermions and fractional quantum Hall effect

hole

Multicomponent fractional quantum Hall states with subband and spin degrees of freedom

systems which brings to life a new \emph{even-denominator} FQHE at

Spin polarization of composite fermions and particle-hole symmetry breaking

\nu=1/2

Observation of an Anisotropic Wigner Crystal.

.

ν = 1 / 2 fractional quantum Hall effect in tilted magnetic fields

In two-dimensional electron systems confined to GaAs quantum wells, as a function of either tilting the sample in a magnetic field or increasing density, we observe multiple spin-polarization transitions of the fractional quantum Hall states at filling factors ν=4/5 and 5/7. The number of observed transitions provides evidence that these are fractional quantum Hall states of interacting two-flux composite fermions. Moreover, the fact that the reentrant integer quantum Hall effect near ν=4/5 always develops following the transition to full spin polarization of the ν=4/5 fractional quantum Hall state links the reentrant phase to a pinned ferromagnetic Wigner crystal of composite fermions.

Geometric Resonance of Composite Fermions Near the ν=1/2 Fractional Quantum Hall State.

We report magnetotransport measurements for the fractional quantum Hall state at filling factor

Anisotropic Composite Fermions and Fractional Quantum Hall Effect

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