41 research outputs found
Anomalous Negative Magnetoresistance Caused by Non-Markovian Effects
A theory of recently discovered anomalous low-field magnetoresistance is
developed for the system of two-dimensional electrons scattered by hard disks
of radius randomly distributed with concentration For small magnetic
fields the magentoresistance is found to be parabolic and inversely
proportional to the gas parameter, With increasing field the magnetoresistance becomes linear
in a good agreement with the
experiment and numerical simulations.Comment: 4 pages RevTeX, 5 figure
Fractional microwave-induced resistance oscillations
We develop a systematic theory of microwave-induced oscillations in
magnetoresistivity of a 2D electron gas in the vicinity of fractional harmonics
of the cyclotron resonance, observed in recent experiments. We show that in the
limit of well-separated Landau levels the effect is dominated by the
multiphoton inelastic mechanism. At moderate magnetic field, two single-photon
mechanisms become important. One of them is due to resonant series of multiple
single-photon transitions, while the other originates from microwave-induced
sidebands in the density of states of disorder-broadened Landau levels.Comment: 3 pages, 2 figures; Proceedings of EP2DS17 to be published in Physica
E; less technical version of arXiv:0707.099
Theory of the oscillatory photoconductivity of a 2D electron gas
We develop a theory of magnetooscillations in the photoconductivity of a
two-dimensional electron gas observed in recent experiments. The effect is
governed by a change of the electron distribution function induced by the
microwave radiation. We analyze a nonlinearity with respect to both the dc
field and the microwave power, as well as the temperature dependence determined
by the inelastic relaxation rate.Comment: 4 pages, 3 figure
Conductivity of 2D many-component electron gas, partially-quantized by magnetic field
The 2D semimetal consisting of heavy holes and light electrons is studied.
The consideration is based on assumption that electrons are quantized by
magnetic field while holes remain classical. We assume also that the
interaction between components is weak and the conversion between components is
absent. The kinetic equation for holes colliding with quantized electrons is
utilized. It has been stated that the inter-component friction and
corresponding correction to the dissipative conductivity {\it do
not vanish at zero temperature} due to degeneracy of the Landau levels. This
correction arises when the Fermi level crosses the Landau level.
The limits of kinetic equation applicability were found. We also study the
situation of kinetic memory when particles repeatedly return to the points of
their meeting.Comment: 13 pages, 1 figur
Stable Monopole-Antimonopole String Background in SU(2) QCD
Motivated by the instability of the Savvidy-Nielsen-Olesen vacuum we make a
systematic search for a stable magnetic background in pure SU(2) QCD. It is
shown that a pair of axially symmetric monopole and antimonopole strings is
stable, provided that the distance between the two strings is less than a
critical value. The existence of a stable monopole-antimonopole string
background strongly supports that a magnetic condensation of
monopole-antimonopole pairs can generate a dynamical symmetry breaking, and
thus the magnetic confinement of color in QCD.Comment: 7 page
High-frequency hopping conductivity in the quantum Hall effect regime: Acoustical studies
The high-frequency conductivity of Si delta-doped GaAs/AlGaAs
heterostructures is studied in the integer quantum Hall effect (QHE) regime,
using acoustic methods. Both the real and the imaginary parts of the complex
conductivity are determined from the experimentally observed magnetic field and
temperature dependences of the velocity and the attenuation of a surface
acoustic wave. It is demonstrated that in the structures studied the mechanism
of low-temperature conductance near the QHE plateau centers is hopping. It is
also shown that at magnetic fields corresponding to filling factors 2 and 4,
the doped Si delta- layer efficiently shunts the conductance in the
two-dimensional electron gas (2DEG) channel. A method to separate the two
contributions to the real part of the conductivity is developed, and the
localization length in the 2DEG channel is estimated.Comment: 8pages, 9 figure
Quasiclassical magnetotransport in a random array of antidots
We study theoretically the magnetoresistance of a
two-dimensional electron gas scattered by a random ensemble of impenetrable
discs in the presence of a long-range correlated random potential. We believe
that this model describes a high-mobility semiconductor heterostructure with a
random array of antidots. We show that the interplay of scattering by the two
types of disorder generates new behavior of which is absent for
only one kind of disorder. We demonstrate that even a weak long-range disorder
becomes important with increasing . In particular, although
vanishes in the limit of large when only one type of disorder is present,
we show that it keeps growing with increasing in the antidot array in the
presence of smooth disorder. The reversal of the behavior of is
due to a mutual destruction of the quasiclassical localization induced by a
strong magnetic field: specifically, the adiabatic localization in the
long-range Gaussian disorder is washed out by the scattering on hard discs,
whereas the adiabatic drift and related percolation of cyclotron orbits
destroys the localization in the dilute system of hard discs. For intermediate
magnetic fields in a dilute antidot array, we show the existence of a strong
negative magnetoresistance, which leads to a nonmonotonic dependence of
.Comment: 21 pages, 13 figure
Faddeev-Niemi Conjecture and Effective Action of QCD
We calculate a one loop effective action of SU(2) QCD in the presence of the
monopole background, and find a possible connection between the resulting QCD
effective action and a generalized Skyrme-Faddeev action of the non-linear
sigma model. The result is obtained using the gauge-independent decomposotion
of the gauge potential into the topological degrees which describes the
non-Abelian monopoles and the local dynamical degrees of the potential, and
integrating out all the dynamical degrees of QCD.Comment: 6 page
Low energy transition in spectral statistics of 2D interactingfermions
We study the level spacing statistics and eigenstate properties of
spinless fermions with Coulomb interaction on a two dimensional lattice at
constant filling factor and various disorder strength. In the limit of large
lattice size, undergoes a transition from the Poisson to the
Wigner-Dyson distribution at a critical total energy independent of the number
of fermions. This implies the emergence of quantum ergodicity induced by
interaction and delocalization in the Hilbert space at zero temperature.Comment: revtex, 5 pages, 4 figures; new data for eigenfunctions are adde