119 research outputs found
Nonconventional odd denominator fractional quantum Hall states in the second Landau level
We report the observation of a new fractional quantum Hall state in the
second Landau level of a two-dimensional electron gas at the Landau level
filling factor . We find that the model of noninteracting composite
fermions can explain the magnitude of gaps of the prominent 2+1/3 and 2+2/3
states. The same model fails, however, to account for the gaps of the 2+2/5 and
the newly observed 2+6/13 states suggesting that these two states are of exotic
origin.omposite fermion model. However, the weaker 2+2/5 and 2+6/13 states
deviate significantly suggesting that these states are of exotic origin
Evidence for the Collective Nature of the Reentrant Integer Quantum Hall States of the Second Landau Level
We report an unexpected sharp peak in the temperature dependence of the
magnetoresistance of the reentrant integer quantum Hall states in the second
Landau level. This peak defines the onset temperature of these states. We find
that in different spin branches the onset temperatures of the reentrant states
scale with the Coulomb energy. This scaling provides direct evidence that
Coulomb interactions play an important role in the formation of these reentrant
states evincing their collective nature
Possible observation of phase coexistence of the fractional quantum Hall liquid and a solid
We have measured the magnetoresistance of a very low density and an extremely
high quality two-dimensional hole system. With increasing magnetic field
applied perpendicularly to the sample we observe the sequence of insulating,
fractional quantum Hall liquid, and insulating phases. In both of the
insulating phases in the vicinity of the filling the
magnetoresistance has an unexpected oscillatory behavior with the magnetic
field. These oscillations are not of the Shubnikov-de Haas type and cannot be
explained by spin effects. They are most likely the consequence of the
formation of a new electronic phase which is intermediate between the
correlated Hall liquid and a disorder pinned solid.Comment: 5 pages, 4 figure
Contrasting Energy Scales of the Reentrant Integer Quantum Hall States
We report drastically different onset temperatures of the reentrant integer
quantum Hall states in the second and third Landau level. This finding is in
quantitative disagreement with the Hartree-Fock theory of the bubble phases
which is thought to describe these reentrant states. Our results indicate that
the number of electrons per bubble in either the second or the third Landau
level is likely different than predicted
Magnetic Field Induced Insulating Phases at Large
Exploring a backgated low density two-dimensional hole sample in the large
regime we found a surprisingly rich phase diagram. At the highest
densities, beside the , 2/3, and 2/5 fractional quantum Hall states,
we observe both of the previously reported high field insulating and reentrant
insulating phases. As the density is lowered, the reentrant insulating phase
initially strengthens, then it unexpectedly starts weakening until it
completely dissapears. At the lowest densities the terminal quantum Hall state
moves from to . The intricate behavior of the insulating
phases can be explained by a non-monotonic melting line in the -
phase space
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