287 research outputs found
Magnetic-Field-Induced Hybridization of Electron Subbands in a Coupled Double Quantum Well
We employ a magnetocapacitance technique to study the spectrum of the soft
two-subband (or double-layer) electron system in a parabolic quantum well with
a narrow tunnel barrier in the centre. In this system unbalanced by gate
depletion, at temperatures T\agt 30 mK we observe two sets of quantum
oscillations: one originates from the upper electron subband in the
closer-to-the-gate part of the well and the other indicates the existence of
common gaps in the spectrum at integer fillings. For the lowest filling factors
and , both the common gap presence down to the point of one- to
two-subband transition and their non-trivial magnetic field dependences point
to magnetic-field-induced hybridization of electron subbands.Comment: Major changes, added one more figure, the latest version to be
published in JETP Let
Shifting the quantum Hall plateau level in a double layer electron system
We study the plateaux of the integer quantum Hall resistance in a bilayer
electron system in tilted magnetic fields. In a narrow range of tilt angles and
at certain magnetic fields, the plateau level deviates appreciably from the
quantized value with no dissipative transport emerging. A qualitative account
of the effect is given in terms of decoupling of the edge states corresponding
to different electron layers/Landau levels.Comment: 3 pages, 3 figures include
Quantum Hall Ferromagnets
It is pointed out recently that the quantum Hall states in bilayer
systems behave like easy plane quantum ferromagnets. We study the
magnetotransport of these systems using their ``ferromagnetic" properties and a
novel spin-charge relation of their excitations. The general transport is a
combination of the ususal Hall transport and a time dependent transport with
time average. The latter is due to a phase slippage process in
and is characterized by two topological constants. (Figures will be
provided upon requests).Comment: 4 pages, Revtex, Ohio State Universit
Evidence for a Goldstone Mode in a Double Layer Quantum Hall System
The tunneling conductance between two parallel 2D electron systems has been
measured in a regime of strong interlayer Coulomb correlations. At total Landau
level filling the tunnel spectrum changes qualitatively when the
boundary separating the compressible phase from the ferromagnetic quantized
Hall state is crossed. A huge resonant enhancement replaces the strongly
suppressed equilibrium tunneling characteristic of weakly coupled layers. The
possible relationship of this enhancement to the Goldstone mode of the broken
symmetry ground state is discussed.Comment: 4 pages, 3 figures, 2 minor typeos fixe
Nonequilibrium phase transition in the kinetic Ising model: Is transition point the maximum lossy point ?
The nonequilibrium dynamic phase transition, in the kinetic Ising model in
presence of an oscillating magnetic field, has been studied both by Monte Carlo
simulation (in two dimension) and by solving the meanfield dynamical equation
of motion for the average magnetization. The temperature variations of
hysteretic loss (loop area) and the dynamic correlation have been studied near
the transition point. The transition point has been identified as the
minimum-correlation point. The hysteretic loss becomes maximum above the
transition point. An analytical formulation has been developed to analyse the
simulation results. A general relationship among hysteresis loop area, dynamic
order parameter and dynamic correlation has also been developed.Comment: 8 pages Revtex and 4 Postscript figures; To appear in Phys. Rev.
Hysteresis and the dynamic phase transition in thin ferromagnetic films
Hysteresis and the non-equilibrium dynamic phase transition in thin magnetic
films subject to an oscillatory external field have been studied by Monte Carlo
simulation. The model under investigation is a classical Heisenberg spin system
with a bilinear exchange anisotropy in a planar thin film geometry with
competing surface fields. The film exhibits a non-equilibrium phase transition
between dynamically ordered and dynamically disordered phases characterized by
a critical temperature Tcd, whose location of is determined by the amplitude H0
and frequency w of the applied oscillatory field. In the presence of competing
surface fields the critical temperature of the ferromagnetic-paramagnetic
transition for the film is suppressed from the bulk system value, Tc, to the
interface localization-delocalization temperature Tci. The simulations show
that in general Tcd < Tci for the model film. The profile of the time-dependent
layer magnetization across the film shows that the dynamically ordered and
dynamically disordered phases coexist within the film for T < Tcd. In the
presence of competing surface fields, the dynamically ordered phase is
localized at one surface of the film.Comment: PDF file, 21 pages including 8 figure pages; added references,typos
added; to be published in PR
Absence of First-order Transition and Tri-critical Point in the Dynamic Phase Diagram of a Spatially Extended Bistable System in an Oscillating Field
It has been well established that spatially extended, bistable systems that
are driven by an oscillating field exhibit a nonequilibrium dynamic phase
transition (DPT). The DPT occurs when the field frequency is on the order of
the inverse of an intrinsic lifetime associated with the transitions between
the two stable states in a static field of the same magnitude as the amplitude
of the oscillating field. The DPT is continuous and belongs to the same
universality class as the equilibrium phase transition of the Ising model in
zero field [G. Korniss et al., Phys. Rev. E 63, 016120 (2001); H. Fujisaka et
al., Phys. Rev. E 63, 036109 (2001)]. However, it has previously been claimed
that the DPT becomes discontinuous at temperatures below a tricritical point
[M. Acharyya, Phys. Rev. E 59, 218 (1999)]. This claim was based on
observations in dynamic Monte Carlo simulations of a multipeaked probability
density for the dynamic order parameter and negative values of the fourth-order
cumulant ratio. Both phenomena can be characteristic of discontinuous phase
transitions. Here we use classical nucleation theory for the decay of
metastable phases, together with data from large-scale dynamic Monte Carlo
simulations of a two-dimensional kinetic Ising ferromagnet, to show that these
observations in this case are merely finite-size effects. For sufficiently
small systems and low temperatures, the continuous DPT is replaced, not by a
discontinuous phase transition, but by a crossover to stochastic resonance. In
the infinite-system limit the stochastic-resonance regime vanishes, and the
continuous DPT should persist for all nonzero temperatures
Generalised Chern-Simons Theory of Composite Fermions in Bilayer Hall Systems
We present a field theory of Jain's composite fermion model as generalised to
the bilayer quantum Hall systems. We define operators which create composite
fermions and write the Hamiltonian exactly in terms of these operators. This is
seen to be a complexified version of the familiar Chern Simons theory. In the
mean-field approximation, the composite fermions feel a modified effective
magnetic field exactly as happens in usual Chern Simons theories, and plateaus
are predicted at the same values of filling factors as Lopez and Fradkin and
Halperin . But unlike normal Chern Simons theories, we obtain all features of
the first-quantised wavefunctions including its phase, modulus and correct
gaussian factors at the mean field level. The familiar Jain relations for
monolayers and the Halperin wavefunction for bilayers come out as special
cases.Comment: Revtex file; 20 pages after processing; no figure
Reentrant Melting of Soliton Lattice Phase in Bilayer Quantum Hall System
At large parallel magnetic field , the ground state of bilayer
quantum Hall system forms uniform soliton lattice phase. The soliton lattice
will melt due to the proliferation of unbound dislocations at certain finite
temperature leading to the Kosterlitz-Thouless (KT) melting. We calculate the
KT phase boundary by numerically solving the newly developed set of Bethe
ansatz equations, which fully take into account the thermal fluctuations of
soliton walls. We predict that within certain ranges of , the
soliton lattice will melt at . Interestingly enough, as temperature
decreases, it melts at certain temperature lower than exhibiting
the reentrant behaviour of the soliton liquid phase.Comment: 11 pages, 2 figure
Correlated few-electron states in vertical double-quantum-dot systems
The electronic properties of semiconductor, vertical, double quantum dot
systems with few electrons are investigated by means of analytic,
configuration-interaction, and mean-field methods. The combined effect of a
high magnetic field, electrostatic confinement, and inter-dot coupling, induces
a new class of few-electron ground states absent in single quantum dots. In
particular, the role played by the isospin (or quantum dot index) in
determining the appearance of new ground states is analyzed and compared with
the role played by the standard spin.Comment: 20 pages, Latex, figures upon request. To appear in Phys. Rev. B
(January 1995
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