29 research outputs found
Magnetotransport in two-dimensional electron gas at large filling factors
We derive the quantum Boltzmann equation for the two-dimensional electron gas
in a magnetic field such that the filling factor . This equation
describes all of the effects of the external fields on the impurity collision
integral including Shubnikov-de Haas oscillations, smooth part of the
magnetoresistance, and non-linear transport. Furthemore, we obtain quantitative
results for the effect of the external microwave radiation on the linear and
non-linear transport in the system. Our findings are relevant for the
description of the oscillating resistivity discovered by Zudov {\em et al.},
zero-resistance state discovered by Mani {\em et al.} and Zudov {\em et al.},
and for the microscopic justification of the model of Andreev {\em et al.}. We
also present semiclassical picture for the qualitative consideration of the
effects of the applied field on the collision integral.Comment: 28 pages, 19 figures; The discussion of the role of the effect of the
microwave field on the distribution function is revised (see also
cond-mat/0310668). Accepted in Phys. Rev.
"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures
We show that in dilute metallic p-SiGe heterostructures, magnetic field can
cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating
states are observed between quantum Hall states with filling factors \nu=1 and
2 and, for the first time, between \nu=2 and 3 and between \nu=4 and 6. The
latter are in contradiction with the original global phase diagram for the
quantum Hall effect. We suggest that the application of a (perpendicular)
magnetic field induces insulating behavior in metallic p-SiGe heterostructures
in the same way as in Si MOSFETs. This insulator is then in competition with,
and interrupted by, integer quantum Hall states leading to the multiple
re-entrant transitions. The phase diagram which accounts for these transition
is similar to that previously obtained in Si MOSFETs thus confirming its
universal character
High-precision molecular dynamics simulation of UO2-PuO2: Anion self-diffusion in UO2
Our series of articles is devoted to high-precision molecular dynamics
simulation of mixed actinide-oxide (MOX) fuel in the approximation of rigid
ions and pair interactions (RIPI) using high-performance graphics processors
(GPU). In this article we study self-diffusion mechanisms of oxygen anions in
uranium dioxide (UO2) with the ten recent and widely used sets of interatomic
pair potentials (SPP) under periodic (PBC) and isolated (IBC) boundary
conditions. Wide range of measured diffusion coefficients (from 10^-3 cm^2/s at
melting point down to 10^-12 cm^2/s at 1400 K) made possible a direct
comparison (without extrapolation) of the simulation results with the
experimental data, which have been known only at low temperatures (T < 1500 K).
A highly detailed (with the temperature step of 1 K) calculation of the
diffusion coefficient allowed us to plot temperature dependences of the
diffusion activation energy and its derivative, both of which show a wide
(~1000 K) superionic transition region confirming the broad lambda-peaks of
heat capacity obtained by us earlier. It is shown that regardless of SPP the
anion self-diffusion in model crystals without surface or artificially embedded
defects goes on via exchange mechanism, rather than interstitial or vacancy
mechanisms suggested by the previous works. The activation energy of exchange
diffusion turned out to coincide with the anti-Frenkel defect formation energy
calculated by the lattice statics.Comment: 18 pages, 11 figures, 5 table
Chiral perturbation theory calculation for pn -> dpipi at threshold
We investigate the reaction pn -> dpipi in the framework of Chiral
Perturbation Theory. For the first time a complete calculation of the leading
order contributions is presented. We identify various diagrams that are of
equal importance as compared to those recognized in earlier works. The diagrams
at leading order behave as expected by the power counting. Also for the first
time the nucleon-nucleon interaction in the initial, intermediate and final
state is included consistently and found to be very important. This study
provides a theoretical basis for a controlled evaluation of the non-resonant
contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table
The First Magnetic Fields
We review current ideas on the origin of galactic and extragalactic magnetic
fields. We begin by summarizing observations of magnetic fields at cosmological
redshifts and on cosmological scales. These observations translate into
constraints on the strength and scale magnetic fields must have during the
early stages of galaxy formation in order to seed the galactic dynamo. We
examine mechanisms for the generation of magnetic fields that operate prior
during inflation and during subsequent phase transitions such as electroweak
symmetry breaking and the quark-hadron phase transition. The implications of
strong primordial magnetic fields for the reionization epoch as well as the
first generation of stars is discussed in detail. The exotic, early-Universe
mechanisms are contrasted with astrophysical processes that generate fields
after recombination. For example, a Biermann-type battery can operate in a
proto-galaxy during the early stages of structure formation. Moreover, magnetic
fields in either an early generation of stars or active galactic nuclei can be
dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also
downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd
Spin Polarization in γd
The study of spin observables is an important and active issue in low energy nuclear physics. In this contribution we report our recent calculation on the γd→
p reaction at low photon energies. Our main goal is to calculate the neutron spin polarization Py′, but we also calculate the total cross section as well as the differential cross section. Although the results for the total and differential cross sections are found to agree reasonably well with the data, the results for Py′ show significant discrepancy with the experiment. We comment on this discrepancy