237 research outputs found
Hysteretic behavior of angular dependence of exchange bias in FeNi/FeMn bilayers
For FeNi/FeMn bilayers, the angular dependence of exchange bias shows hysteresis between clockwise and counterclockwise rotations, as a new signature. The hysteresis decreases for thick antiferromagnet layers. Calculations have clearly shown that the orientation of antiferromagnet spins also exhibits hysteresis between clockwise and counterclockwise rotations. This furnishes an interpretation of the macroscopic behavior of the ferromagnetic layer in terms of the thermally driven evolution of the magnetic state of the antiferromagnet layer
Rotation of the pinning direction in the exchange bias training effect in polycrystalline NiFe/FeMn bilayers
For polycrystalline NiFe/FeMn bilayers, we have observed and quantified the rotation of the pinning direction in the exchange bias training and recovery effects. During consecutive hysteresis loops, the rotation of the pinning direction strongly depends on the magnetization reversal mechanism of the ferromagnet layer. The interfacial uncompensated magnetic moment of antiferromagnetic grains may be irreversibly switched and rotated when the magnetization reversal process of the ferromagnet layer is accompanied by domain wall motion and domain rotation, respectively
Magnetization and Level Statistics at Quantum Hall Liquid-Insulator Transition in the Lattice Model
Statistics of level spacing and magnetization are studied for the phase
diagram of the integer quantum Hall effect in a 2D finite lattice model with
Anderson disorder.Comment: 4 pages, 6 figure
The Vacuum System of HIRFL
AbstractThe vacuum system of Heavy Ion Research Facility in Lanzhou (HIRFL) is a large and complex system. HIRFL consists of two ECR ion sources, a sector focus cyclotron (SFC), a separate sector cyclotron (SSC) and a multi-purpose cooling storage ring system which has a main ring (CSRm) and an experiment ring (CSRe). Several beam lines connect these accelerators together and transfer various heavy ion beams to more than 10 experiment terminals. According to the requirements of the ion acceleration and ion lifetime, the working pressure in each accelerator is different. SFC is nearly 50 years old. After upgrade, the working pressure in SFC is improved from 10-6mbar to 10-8mbar. The pressure in SSC which was built in the 1980s reaches the same level. The cooling storage ring system with a length of 500m came into operation in 2007. The average pressures in CSRm and CSRe are 5×10-12mbar and 8×10-12mbar respectively. Different designs were adopt for vacuum system of a dozen beam lines to meet specific requirement of each experiment terminal. Along with the extensive development of the heavy ion researches and applications, new accelerators of HIRFL are under construction. The vacuum system of the new machines will be designed and constructed followed the overall schedule
Quantifying the levitation picture of extended states in lattice models
The behavior of extended states is quantitatively analyzed for two
dimensional lattice models. A levitation picture is established for both
white-noise and correlated disorder potentials. In a continuum limit window of
the lattice models we find simple quantitative expressions for the extended
states levitation, suggesting an underlying universal behavior. On the other
hand, these results point out that the Quantum Hall phase diagrams may be
disorder dependent.Comment: 5 pages, submitted to PR
Levitation of quantum Hall critical states in a lattice model with spatially correlated disorder
The fate of the current carrying states of a quantum Hall system is
considered in the situation when the disorder strength is increased and the
transition from the quantum Hall liquid to the Hall insulator takes place. We
investigate a two-dimensional lattice model with spatially correlated disorder
potentials and calculate the density of states and the localization length
either by using a recursive Green function method or by direct diagonalization
in connection with the procedure of level statistics. From the knowledge of the
energy and disorder dependence of the localization length and the density of
states (DOS) of the corresponding Landau bands, the movement of the current
carrying states in the disorder--energy and disorder--filling-factor plane can
be traced by tuning the disorder strength.
We show results for all sub-bands, particularly the traces of the Chern and
anti-Chern states as well as the peak positions of the DOS. For small disorder
strength we recover the well known weak levitation of the critical states,
but we also reveal, for larger , the strong levitation of these states
across the Landau gaps without merging. We find the behavior to be similar for
exponentially, Gaussian, and Lorentzian correlated disorder potentials. Our
study resolves the discrepancies of previously published work in demonstrating
the conflicting results to be only special cases of a general lattice model
with spatially correlated disorder potentials.
To test whether the mixing between consecutive Landau bands is the origin of
the observed floating, we truncate the Hilbert space of our model Hamiltonian
and calculate the behavior of the current carrying states under these
restricted conditions.Comment: 10 pages, incl. 13 figures, accepted for publication in PR
SQCD: A Geometric Apercu
We take new algebraic and geometric perspectives on the old subject of SQCD.
We count chiral gauge invariant operators using generating functions, or
Hilbert series, derived from the plethystic programme and the Molien-Weyl
formula. Using the character expansion technique, we also see how the global
symmetries are encoded in the generating functions. Equipped with these methods
and techniques of algorithmic algebraic geometry, we obtain the character
expansions for theories with arbitrary numbers of colours and flavours.
Moreover, computational algebraic geometry allows us to systematically study
the classical vacuum moduli space of SQCD and investigate such structures as
its irreducible components, degree and syzygies. We find the vacuum manifolds
of SQCD to be affine Calabi-Yau cones over weighted projective varieties.Comment: 49 pages, 1 figur
Ballistic electron motion in a random magnetic field
Using a new scheme of the derivation of the non-linear -model we
consider the electron motion in a random magnetic field (RMF) in two
dimensions. The derivation is based on writing quasiclassical equations and
representing their solutions in terms of a functional integral over
supermatrices with the constraint . Contrary to the standard scheme,
neither singling out slow modes nor saddle-point approximation are used. The
-model obtained is applicable at the length scale down to the electron
wavelength. We show that this model differs from the model with a random
potential (RP).However, after averaging over fluctuations in the Lyapunov
region the standard -model is obtained leading to the conventional
localization behavior.Comment: 10 pages, no figures, to be submitted in PRB v2: Section IV is
remove
Quantum Locality
It is argued that while quantum mechanics contains nonlocal or entangled
states, the instantaneous or nonlocal influences sometimes thought to be
present due to violations of Bell inequalities in fact arise from mistaken
attempts to apply classical concepts and introduce probabilities in a manner
inconsistent with the Hilbert space structure of standard quantum mechanics.
Instead, Einstein locality is a valid quantum principle: objective properties
of individual quantum systems do not change when something is done to another
noninteracting system. There is no reason to suspect any conflict between
quantum theory and special relativity.Comment: Introduction has been revised, references added, minor corrections
elsewhere. To appear in Foundations of Physic
Hidden degree of freedom and critical states in a two-dimensional electron gas in the presence of a random magnetic field
We establish the existence of a hidden degree of freedom and the critical
states of a spinless electron system in a spatially-correlated random magnetic
field with vanishing mean. Whereas the critical states are carried by the
zero-field contours of the field landscape, the hidden degree of freedom is
recognized as being associated with the formation of vortices in these special
contours. It is argued that, as opposed to the coherent backscattering
mechanism of weak localization, a new type of scattering processes in the
contours controls the underlying physics of localization in the random magnetic
field system. In addition, we investigate the role of vortices in governing the
metal-insulator transition and propose a renormalization-group diagram for the
system under study.Comment: 17 pages, 16 figures; Figs. 1, 7, 9, and 10 have been reduced in
quality for e-submissio
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