1,714 research outputs found
Quantum Spectra and Wave Functions in Terms of Periodic Orbits for Weakly Chaotic Systems
Special quantum states exist which are quasiclassical quantizations of
regions of phase space that are weakly chaotic. In a weakly chaotic region, the
orbits are quite regular and remain in the region for some time before escaping
and manifesting possible chaotic behavior. Such phase space regions are
characterized as being close to periodic orbits of an integrable reference
system. The states are often rather striking, and can be concentrated in
spatial regions. This leads to possible phenomena. We review some methods we
have introduced to characterize such regions and find analytic formulas for the
special states and their energies.Comment: 9 pages, 8 eps figure
Electron correlations and single-particle physics in the Integer Quantum Hall Effect
The compressibility of a two-dimensional electron system with spin in a
spatially correlated random potential and a quantizing magnetic field is
investigated. Electron-electron interaction is treated with the Hartree-Fock
method. Numerical results for the influences of interaction and disorder on the
compressibility as a function of the particle density and the strength of the
magnetic field are presented. Localization-delocalization transitions
associated with highly compressible region in the energy spectrum are found at
half-integer filling factors. Coulomb blockade effects are found near integer
fillings in the regions of low compressibility. Results are compared with
recent experiments.Comment: 4 pages, 2 figures, replaced with revised versio
Imaging Transport Resonances in the Quantum Hall Effect
We use a scanning capacitance probe to image transport in the quantum Hall
system. Applying a DC bias voltage to the tip induces a ring-shaped
incompressible strip (IS) in the 2D electron system (2DES) that moves with the
tip. At certain tip positions, short-range disorder in the 2DES creates a
quantum dot island in the IS. These islands enable resonant tunneling across
the IS, enhancing its conductance by more than four orders of magnitude. The
images provide a quantitative measure of disorder and suggest resonant
tunneling as the primary mechanism for transport across ISs.Comment: 4 pages, 4 figures, submitted to PRL. For movies and additional
infomation, see http://electron.mit.edu/scanning/; Added scale bars to
images, revised discussion of figure 3, other minor change
Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system
We report the experimental observation of the spin-Hall effect in a
two-dimensional (2D) hole system with Rashba spin-orbit coupling.
The 2D hole layer is a part of a p-n junction light-emitting diode with a
specially designed co-planar geometry which allows an angle-resolved
polarization detection at opposite edges of the 2D hole system. In equilibrium
the angular momenta of the Rashba split heavy hole states lie in the plane of
the 2D layer. When an electric field is applied across the hole channel a non
zero out-of-plane component of the angular momentum is detected whose sign
depends on the sign of the electric field and is opposite for the two edges.
Microscopic quantum transport calculations show only a weak effect of disorder
suggesting that the clean limit spin-Hall conductance description (intrinsic
spin-Hall effect) might apply to our system.Comment: 4 pages, 3 figures, paper based on work presented at the Gordon
Research Conference on Magnetic Nano-structures (August 2004) and Oxford Kobe
Seminar on Spintronics (September 2004); accepted for publication in Physical
Review Letters December 200
Non-Abelian Braiding of Lattice Bosons
We report on a numerical experiment in which we use time-dependent potentials
to braid non-abelian quasiparticles. We consider lattice bosons in a uniform
magnetic field within the fractional quantum Hall regime, where , the
ratio of particles to flux quanta, is near 1/2, 1 or 3/2. We introduce
time-dependent potentials which move quasiparticle excitations around one
another, explicitly simulating a braiding operation which could implement part
of a gate in a quantum computation. We find that different braids do not
commute for near and , with Berry matrices respectively
consistent with Ising and Fibonacci anyons. Near , the braids commute.Comment: 5 pages, 1 figur
Anyon Condensation and Continuous Topological Phase Transitions in Non-Abelian Fractional Quantum Hall States
We find a series of possible continuous quantum phase transitions between
fractional quantum Hall (FQH) states at the same filling fraction in
two-component quantum Hall systems. These can be driven by tuning the
interlayer tunneling and/or interlayer repulsion. One side of the transition is
the Halperin (p,p,p-3) Abelian two-component state while the other side is the
non-Abelian Z4 parafermion (Read-Rezayi) state. We predict that the transition
is a continuous transition in the 3D Ising class. The critical point is
described by a Z2 gauged Ginzburg-Landau theory. These results have
implications for experiments on two-component systems at \nu = 2/3 and
single-component systems at \nu = 8/3.Comment: 4 pages + ref
Optical Hall Effect in the Integer Quantum Hall Regime
Optical Hall conductivity is measured from the Faraday
rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz
frequency regime. The Faraday rotation angle ( fine structure constant
mrad) is found to significantly deviate from the Drude-like behavior to
exhibit a plateau-like structure around the Landau-level filling . The
result, which fits with the behavior expected from the carrier localization
effect in the ac regime, indicates that the plateau structure, although not
quantized, still exists in the terahertz regime.Comment: 4 pages, 4 figure
- …