127 research outputs found
Extra Current and Integer Quantum Hall Conductance in the Spin-Orbit Coupling System
We study the extra term of particle current in a 2D k-cubic Rashba spin-orbit
coupling system and the integer quantization of the Hall conductance in this
system. We provide a correct formula of charge current in this system and the
careful consideration of extra currents provides a stronger theoretical basis
for the theory of the quantum Hall effect which has not been considered before.
The non-trivial extra contribution to the particle current density and local
conductivity, which originates from the cubic dependence on the momentum
operator in the Hamiltonian, will have no effect on the integer quantization of
the Hall conductance. The extension of Noether's theorem for the 2D k-cubic
Rashba system is also addressed. The two methods reach to exactly the same
results.Comment: 6 page
Quantum Electrodynamics and the Origins of the Exchange, Dipole-Dipole, and Dzyaloshinsky-Moriya Interactions in Itinerant Fermion Systems
It is shown how the exchange interaction, the dipole-dipole interaction, and
the Dzyaloshinsky-Moriya interaction between electronic spin-density
fluctuations emerge naturally from a field-theoretic framework that couples
electrons to the fluctuating electromagnetic potential. Semi-quantitative
estimates are given to determine when the dipole-dipole interaction, which is
often neglected, needs to be considered, and various applications are
discussed, with an emphasis on weak ferromagnets and on helimagnets.Comment: 12pp, 3 fig
Microscopic Aspects of Stretched Exponential Relaxation (SER) in Homogeneous Molecular and Network Glasses and Polymers
Because the theory of SER is still a work in progress, the phenomenon itself
can be said to be the oldest unsolved problem in science, as it started with
Kohlrausch in 1847. Many electrical and optical phenomena exhibit SER with
probe relaxation I(t) ~ exp[-(t/{\tau}){\beta}], with 0 < {\beta} < 1. Here
{\tau} is a material-sensitive parameter, useful for discussing chemical
trends. The "shape" parameter {\beta} is dimensionless and plays the role of a
non-equilibrium scaling exponent; its value, especially in glasses, is both
practically useful and theoretically significant. The mathematical complexity
of SER is such that rigorous derivations of this peculiar function were not
achieved until the 1970's. The focus of much of the 1970's pioneering work was
spatial relaxation of electronic charge, but SER is a universal phenomenon, and
today atomic and molecular relaxation of glasses and deeply supercooled liquids
provide the most reliable data. As the data base grew, the need for a
quantitative theory increased; this need was finally met by the
diffusion-to-traps topological model, which yields a remarkably simple
expression for the shape parameter {\beta}, given by d*/(d* + 2). At first
sight this expression appears to be identical to d/(d + 2), where d is the
actual spatial dimensionality, as originally derived. The original model,
however, failed to explain much of the data base. Here the theme of earlier
reviews, based on the observation that in the presence of short-range forces
only d* = d = 3 is the actual spatial dimensionality, while for mixed short-
and long-range forces, d* = fd = d/2, is applied to four new spectacular
examples, where it turns out that SER is useful not only for purposes of
quality control, but also for defining what is meant by a glass in novel
contexts. (Please see full abstract in main text
High-Resolution Simulations of Convection Preceding Ignition in Type Ia Supernovae Using Adaptive Mesh Refinement
We extend our previous three-dimensional, full-star simulations of the final
hours of convection preceding ignition in Type Ia supernovae to higher
resolution using the adaptive mesh refinement capability of our low Mach number
code, MAESTRO. We report the statistics of the ignition of the first flame at
an effective 4.34 km resolution, and general flow field properties at an
effective 2.17 km resolution. We find that off-center ignition is likely, with
radius of 50 km most favored and a likely range of 40 to 75 km. This is
consistent with our previous coarser (8.68 km resolution) simulations, implying
that we have achieved sufficient resolution in our determination of likely
ignition radii. The dynamics of the last few hot spots preceding ignition
suggest that a multiple ignition scenario is not likely. With improved
resolution, we can more clearly see the general flow pattern in the convective
region, characterized by a strong outward plume with a lower speed
recirculation. We show that the convective core is turbulent with a Kolmogorov
spectrum and has a lower turbulent intensity and larger integral length scale
than previously thought (on the order of 16 km s and 200 km,
respectively), and we discuss the potential consequences for the first flames.Comment: Accepted to ApJ. 48 pages. Some figures degraded to conserve spac
Strong interface-induced spin-orbit coupling in graphene on WS2
Interfacial interactions allow the electronic properties of graphene to be
modified, as recently demonstrated by the appearance of satellite Dirac cones
in the band structure of graphene on hexagonal boron nitride (hBN) substrates.
Ongoing research strives to explore interfacial interactions in a broader class
of materials in order to engineer targeted electronic properties. Here we show
that at an interface with a tungsten disulfide (WS2) substrate, the strength of
the spin-orbit interaction (SOI) in graphene is very strongly enhanced. The
induced SOI leads to a pronounced low-temperature weak anti-localization (WAL)
effect, from which we determine the spin-relaxation time. We find that
spin-relaxation time in graphene is two-to-three orders of magnitude smaller on
WS2 than on SiO2 or hBN, and that it is comparable to the intervalley
scattering time. To interpret our findings we have performed first-principle
electronic structure calculations, which both confirm that carriers in
graphene-on-WS2 experience a strong SOI and allow us to extract a
spin-dependent low-energy effective Hamiltonian. Our analysis further shows
that the use of WS2 substrates opens a possible new route to access topological
states of matter in graphene-based systems.Comment: Originally submitted version in compliance with editorial guidelines.
Final version with expanded discussion of the relation between theory and
experiments to be published in Nature Communication
Spin dynamics in semiconductors
This article reviews the current status of spin dynamics in semiconductors
which has achieved a lot of progress in the past years due to the fast growing
field of semiconductor spintronics. The primary focus is the theoretical and
experimental developments of spin relaxation and dephasing in both spin
precession in time domain and spin diffusion and transport in spacial domain. A
fully microscopic many-body investigation on spin dynamics based on the kinetic
spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published
in Physics Reports
The role of GRK6 in animal models of Parkinson's Disease and L-DOPA treatment
G protein-coupled Receptor Kinase 6 (GRK6) belongs to a family of kinases that phosphorylate GPCRs. GRK6 levels were found to be altered in Parkinson's Disease (PD) and D2 dopamine receptors are supersensitive in mice lacking GRK6 (GRK6-KO mice). To understand how GRK6 modulates the behavioral manifestations of dopamine deficiency and responses to L-DOPA, we used three approaches to model PD in GRK6-KO mice: 1) the cataleptic response to haloperidol; 2) introducing GRK6 mutation to an acute model of absolute dopamine deficiency, DDD mice; 3) hemiparkinsonian 6-OHDA model. Furthermore, dopamine-related striatal signaling was analyzed by assessing the phosphorylation of AKT/GSK3ÎČ and ERK1/2. GRK6 deficiency reduced cataleptic behavior, potentiated the acute effect of L-DOPA in DDD mice, reduced rotational behavior in hemi-parkinsonian mice, and reduced abnormal involuntary movements induced by chronic L-DOPA. These data indicate that approaches to regulate GRK6 activity could be useful in modulating both therapeutic and side-effects of L-DOPA
One-Dimensional Fermi liquids
I attempt to give a pedagogical overview of the progress which has occurred
during the past decade in the description of one-dimensional correlated
fermions. Fermi liquid theory based on a quasi-particle picture, breaks down in
one dimension because of the Peierls divergence and because of charge-spin
separation. It is replaced by a Luttinger liquid whose elementary excitations
are collective charge and spin modes, based on the exactly solvable Luttinger
model. I review this model and various solutions with emphasis on bosonization
(and its equivalence to conformal field theory), and its physical properties.
The notion of a Luttinger liquid implies that all gapless 1D systems share
these properties at low energies.
Chapters 1 and 2 of the article contain an introduction and a discussion of
the breakdown of Fermi liquid theory. Chapter 3 describes in detail the
solution of the Luttinger model both by bosonization and by Green's functions
methods and summarizes the properties of the model, expressed thorugh
correlation functions. The relation to conformal field theory is discussed.
Chapter 4 of the article introduces the notion of a Luttinger liquid. It
describes in much detail the various mappings applied to realistic models of 1D
correlated fermions, onto the Luttinger model, as well as important corrections
to the Luttinger model properties discussed in Ch.3. Chapter 5 describes
situations where the Luttinger liquid is not a stable fixed point, and where
spin or charge gaps open in at least one channel. Chapter 6 discusses
multi-band and multichain problems, in particular the stability of a Luttinger
liquid with respect to interchain hopping. Ch. 7 gives a brief summary of
experimental efforts to uncover Luttinger liquid correlations in quasi-1D
materials.Comment: uuencoded Latex files and postscript figures, one Readme-file approx
160 pages + 13 figures; to be published by Reports on Progress in Physic
Review of Particle Physics
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances.
The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings.
The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version optimized for use on phones, and as an Android app
Review of Particle Physics
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,062 new measurements from 721 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 117 reviews are many that are new or heavily revised, including those on Pentaquarks and Inflation. The complete Review is published online in a journal and on the website of the Particle Data Group (http://pdg.lbl.gov). The printed PDG Book contains the Summary Tables and all review articles but no longer includes the detailed tables from the Particle Listings. A Booklet with the Summary Tables and abbreviated versions of some of the review articles is also available
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