2,908 research outputs found
Possible Reentrance of the Fractional Quantum Hall Effect in the Lowest Landau Level
In the framework of a recently developed model of interacting composite
fermions, we calculate the energy of different solid and Laughlin-type liquid
phases of spin-polarized composite fermions. The liquid phases have a lower
energy than the competing solids around the electronic filling factors
nu=4/11,6/17, and 4/19 and may thus be responsible for the fractional quantum
Hall effect at nu=4/11. The alternation between solid and liquid phases when
varying the magnetic field may lead to reentrance phenomena in analogy with the
observed reentrant integral quantum Hall effect.Comment: 4 pages, 3 figures; revised version accepted for publication in Phys.
Rev. Let
Second Generation of Composite Fermions and the Self-Similarity of the Fractional Quantum Hall Effect
A recently developed model of interacting composite fermions, is used to
investigate different composite-fermion phases. Their interaction potential
allows for the formation of both solid and new quantum-liquid phases, which are
interpreted in terms of second-generation composite fermions and which may be
responsible for the fractional quantum Hall states observed at unusual filling
factors, such as nu=4/11. Projection of the composite-fermion dynamics to a
single level, involved in the derivation of the Hamiltonian of interacting
composite fermions, reveals the underlying self-similarity of the model.Comment: 4 pages, 1 figure; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)", only change with respect to v1: correction in authors line, no
changes in manuscrip
Quantum Phases in Partially Filled Landau Levels
We compare the energies of different electron solids, such as bubble crystals
with triangular and square symmetry and stripe phases, to those of correlated
quantum liquids in partially filled intermediate Landau levels. Multiple
transitions between these phases when varying the filling of the top-most
partially filled Landau level explain the observed reentrance of the integer
quantum Hall effect. The phase transitions are identified as first-order. This
leads to a variety of measurable phenomena such as the phase coexistence
between a Wigner crystal and a two-electron bubble phase in a Landau-level
filling-factor range , which has recently been observed in
transport measurements under micro-wave irradiation.Comment: 6 pages, 2 figures; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)
Local density of states of electron-crystal phases in graphene in the quantum Hall regime
We calculate, within a self-consistent Hartree-Fock approximation, the local
density of states for different electron crystals in graphene subject to a
strong magnetic field. We investigate both the Wigner crystal and bubble
crystals with M_e electrons per lattice site. The total density of states
consists of several pronounced peaks, the number of which in the negative
energy range coincides with the number of electrons M_e per lattice site, as
for the case of electron-solid phases in the conventional two-dimensional
electron gas. Analyzing the local density of states at the peak energies, we
find particular scaling properties of the density patterns if one fixes the
ratio nu_N/M_e between the filling factor nu_N of the last partially filled
Landau level and the number of electrons per bubble. Although the total density
profile depends explicitly on M_e, the local density of states of the lowest
peaks turns out to be identical regardless the number of electrons M_e. Whereas
these electron-solid phases are reminiscent to those expected in the
conventional two-dimensional electron gas in GaAs heterostructures in the
quantum Hall regime, the local density of states and the scaling relations we
highlight in this paper may be, in graphene, directly measured by spectroscopic
means, such as e.g. scanning tunneling microscopy.Comment: 8 pages, 7 figures; minor correction
Scaling Approach to the Phase Diagram of Quantum Hall Systems
We present a simple classification of the different liquid and solid phases
of quantum Hall systems in the limit where the Coulomb interaction between the
electrons is significant, i.e. away from integral filling factors. This
classification, and a criterion for the validity of the mean-field
approximation in the charge-density-wave phase, is based on scaling arguments
concerning the effective interaction potential of electrons restricted to an
arbitrary Landau level. Finite-temperature effects are investigated within the
same formalism, and a good agreement with recent experiments is obtained.Comment: 4 pages, 3 figures; to be published in Europhys. Lett.; new version
contains more detailed description of finite-temperature effect
On the self-similarity in quantum Hall systems
The Hall-resistance curve of a two-dimensional electron system in the
presence of a strong perpendicular magnetic field is an example of
self-similarity. It reveals plateaus at low temperatures and has a fractal
structure. We show that this fractal structure emerges naturally in the
Hamiltonian formulation of composite fermions. After a set of transformations
on the electronic model, we show that the model, which describes interacting
composite fermions in a partially filled energy level, is self-similar. This
mathematical property allows for the construction of a basis of higher
generations of composite fermions. The collective-excitation dispersion of the
recently observed 4/11 fractional-quantum-Hall state is discussed within the
present formalism.Comment: 7 pages, 4 figures; version accepted for publication in Europhys.
Lett., new version contains energy calculations for collective excitations of
the 4/11 stat
Staircase to Higher-Order Topological Phase Transitions
We find a series of topological phase transitions of increasing order, beyond
the more standard second-order phase transition in a one-dimensional
topological superconductor. The jumps in the order of the transitions depend on
the range of the pairing interaction, which is parametrized by an algebraic
decay with exponent . Remarkably, in the limit the order
of the topological transition becomes infinite. We compute the critical
exponents for the series of higher-order transitions in exact form and find
that they fulfill the hyperscaling relation. We also study the critical
behaviour at the boundary of the system and discuss potential experimental
platforms of magnetic atoms in superconductors.Comment: 5+5pages, 7 figures. Accepted as a Rapid Communicatio
Dynamics of topological defects in a spiral: a scenario for the spin-glass phase of cuprates
We propose that the dissipative dynamics of topological defects in a spiral
state is responsible for the transport properties in the spin-glass phase of
cuprates. Using the collective-coordinate method, we show that topological
defects are coupled to a bath of magnetic excitations. By integrating out the
bath degrees of freedom, we find that the dynamical properties of the
topological defects are dissipative. The calculated damping matrix is related
to the in-plane resistivity, which exhibits an anisotropy and linear
temperature dependence in agreement with experimental data.Comment: 4 pages, as publishe
Finite-momentum Bose-Einstein condensates in shaken 2D square optical lattices
We consider ultracold bosons in a 2D square optical lattice described by the
Bose-Hubbard model. In addition, an external time-dependent sinusoidal force is
applied to the system, which shakes the lattice along one of the diagonals. The
effect of the shaking is to renormalize the nearest-neighbor hopping
coefficients, which can be arbitrarily reduced, can vanish, or can even change
sign, depending on the shaking parameter. It is therefore necessary to account
for higher-order hopping terms, which are renormalized differently by the
shaking, and introduce anisotropy into the problem. We show that the
competition between these different hopping terms leads to finite-momentum
condensates, with a momentum that may be tuned via the strength of the shaking.
We calculate the boundaries between the Mott-insulator and the different
superfluid phases, and present the time-of-flight images expected to be
observed experimentally. Our results open up new possibilities for the
realization of bosonic analogs of the FFLO phase describing inhomogeneous
superconductivity.Comment: 7 pages, 7 figure
Chern-Simons theory of multi-component quantum Hall systems
The Chern-Simons approach has been widely used to explain fractional quantum
Hall states in the framework of trial wave functions. In the present paper, we
generalise the concept of Chern-Simons transformations to systems with any
number of components (spin or pseudospin degrees of freedom), extending earlier
results for systems with one or two components. We treat the density
fluctuations by adding auxiliary gauge fields and appropriate constraints. The
Hamiltonian is quadratic in these fields and hence can be treated as a harmonic
oscillator Hamiltonian, with a ground state that is connected to the Halperin
wave functions through the plasma analogy. We investigate several conditions on
the coefficients of the Chern-Simons transformation and on the filling factors
under which our model is valid. Furthermore, we discuss several singular cases,
associated with symmetric states.Comment: 11 pages, shortened version, accepted for publication in Phys. Rev.
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