1,450 research outputs found
Magnetically Robust Non-Fermi Liquid Behavior in Heavy Fermion Systems with f^2-Configuration: Competition between Crystalline-Electric-Field and Kondo-Yosida Singlets
We study a magnetic field effect on the Non-Fermi Liquid (NFL) which arises
around the quantum critical point (QCP) due to the competition between the
f^2-crystalline-electric-field singlet and the Kondo-Yosida singlet states by
using the numerical renormalization ground method. We show the characteristic
temperature T_F^*, corresponding to a peak of a specific heat, is not affected
by the magnetic field up to H_z^* which is determined by the distance from the
QCP or characteristic energy scales of each singlet states. As a result, in the
vicinity of QCP, there are parameter regions where the NFL is robust against
the magnetic field, at an observable temperature range T > T_F^*, up to H_z^*
which is far larger than T_F^* and less than min(T_{K2}, $Delta).Comment: 8 pages, 9 figur
Selforganized 3-band structure of the doped fermionic Ising spin glass
The fermionic Ising spin glass is analyzed for arbitrary filling and for all
temperatures. A selforganized 3-band structure of the model is obtained in the
magnetically ordered phase. Deviation from half filling generates a central
nonmagnetic band, which becomes sharply separated at T=0 by (pseudo)gaps from
upper and lower magnetic bands. Replica symmetry breaking effects are derived
for several observables and correlations. They determine the shape of the
3-band DoS, and, for given chemical potential, influence the fermion filling
strongly in the low temperature regime.Comment: 13 page
Methanol masers probing the ordered magnetic field of W75N
The role of magnetic fields during the protostellar phase of high-mass
star-formation is a debated topic. In particular, it is still unclear how
magnetic fields influence the formation and dynamic of disks and outflows. Most
current information on magnetic fields close to high-mass protostars comes from
H2O and OH maser observations. Recently, the first 6.7 GHz methanol maser
polarization observations were made, and they reveal strong and ordered
magnetic fields. The morphology of the magnetic field during high-mass
star-formation needs to be investigated on small scales, which can only be done
using very long baseline interferometry observations. The massive star-forming
regionW75N contains three radio sources and associated masers, while a
large-scale molecular bipolar outflow is also present. Polarization
observations of the 6.7 GHz methanol masers at high angular resolution probe
the strength and structure of the magnetic field and determine its relation to
the outflow. Eight of the European VLBI network antennas were used to measure
the linear polarization and Zeeman-splitting of the 6.7 GHz methanol masers in
the star-forming region W75N. We detected 10 methanol maser features, 4 of
which were undetected in previous work. All arise near the source VLA1 of W75N.
The linear polarization of the masers reveals a tightly ordered magnetic field
over more than 2000 AU around VLA1 that is exactly aligned with the large-scale
molecular outflow. This is consistent with the twisted magnetic field model
proposed for explaining dust polarization observations. The Zeeman-splitting
measured on 3 of the maser features indicates a dynamically important magnetic
field in the maser region of the order of 50mG. We suggest VLA1 is the powering
sources of the bipolar outflow.Comment: 5 pages, 3 figures, accepted by Astronomy and Astrophysic
Critical Nature of Non-Fermi Liquid in Spin 3/2 Multipolar Kondo Model
A multipolar Kondo model of an impurity spin S_I=3/2 interacting with
conduction electrons with spin s_c=3/2 is investigated using boundary conformal
field theory. A two-channel Kondo (2CK) -like non-Fermi liquid (NFL) under the
particle-hole symmetry is derived explicitly using a ``superspin absorption''
in the sector of a hidden symmetry, SO(5). We discuss the difference between
the usual spin-1/2 2CK NFL fixed point and the present one. In particular, we
find that, unlike the usual 2CK model, the low temperature impurity specific
heat is proportional to temperature.Comment: 4 pages, 2 figure
Evidence for a Massive Protocluster in S255N
S255N is a luminous far-infrared source that contains many indications of
active star formation but lacks a prominent near-infrared stellar cluster. We
present mid-infrared through radio observations aimed at exploring the
evolutionary state of this region. Our observations include 1.3mm continuum and
spectral line data from the Submillimeter Array, VLA 3.6cm continuum and 1.3cm
water maser data, and multicolor IRAC images from the Spitzer Space Telescope.
The cometary morphology of the previously-known UCHII region G192.584-0.041 is
clearly revealed in our sensitive, multi-configuration 3.6cm images. The 1.3mm
continuum emission has been resolved into three compact cores, all of which are
dominated by dust emission and have radii < 7000AU. The mass estimates for
these cores range from 6 to 35 Msun. The centroid of the brightest dust core
(SMA1) is offset by 1.1'' (2800 AU) from the peak of the cometary UCHII region
and exhibits the strongest HC3N, CN, and DCN line emission in the region. SMA1
also exhibits compact CH3OH, SiO, and H2CO emission and likely contains a young
hot core. We find spatial and kinematic evidence that SMA1 may contain further
multiplicity, with one of the components coincident with a newly-detected H2O
maser. There are no mid-infrared point source counterparts to any of the dust
cores, further suggesting an early evolutionary phase for these objects. The
dominant mid-infrared emission is a diffuse, broadband component that traces
the surface of the cometary UCHII region but is obscured by foreground material
on its southern edge. An additional 4.5 micron linear feature emanating to the
northeast of SMA1 is aligned with a cluster of methanol masers and likely
traces a outflow from a protostar within SMA1. Our observations provide direct
evidence that S255N is forming a cluster of intermediate to high-mass stars.Comment: 34 pages, 11 figures, accepted for publication in The Astronomical
Journa
Enhancement of the Two-channel Kondo Effect in Single-Electron boxes
The charging of a quantum box, coupled to a lead by tunneling through a
single resonant level, is studied near the degeneracy points of the Coulomb
blockade. Combining Wilson's numerical renormalization-group method with
perturbative scaling approaches, the corresponding low-energy Hamiltonian is
solved for arbitrary temperatures, gate voltages, tunneling rates, and energies
of the impurity level. Similar to the case of a weak tunnel barrier, the shape
of the charge step is governed at low temperatures by the non-Fermi-liquid
fixed point of the two-channel Kondo effect. However, the associated Kondo
temperature TK is strongly modified. Most notably, TK is proportional to the
width of the level if the transmission through the impurity is close to unity
at the Fermi energy, and is no longer exponentially small in one over the
tunneling matrix element. Focusing on a particle-hole symmetric level, the
two-channel Kondo effect is found to be robust against the inclusion of an
on-site repulsion on the level. For a large on-site repulsion and a large
asymmetry in the tunneling rates to box and to the lead, there is a sequence of
Kondo effects: first the local magnetic moment that forms on the level
undergoes single-channel screening, followed by two-channel overscreening of
the charge fluctuations inside the box.Comment: 21 pages, 19 figure
Low energy fixed points of the sigma-tau and the O(3) symmetric Anderson models
We study the single channel (compactified) models, the sigma-tau model and
the O(3) symmetric Anderson model, which were introduced by Coleman et al., and
Coleman and Schofield, as a simplified way to understand the low energy
behaviour of the isotropic and anisotropic two channel Kondo systems. These
models display both Fermi liquid and marginal Fermi liquid behaviour and an
understanding of the nature of their low energy fixed points may give some
general insights into the low energy behaviour of other strongly correlated
systems. We calculate the excitation spectrum at the non-Fermi liquid fixed
point of the sigma-tau model using conformal field theory, and show that the
results are in agreement with those obtained in recent numerical
renormalization group (NRG) calculations. For the O(3) Anderson model we find
further logarithmic corrections in the weak coupling perturbation expansion to
those obtained in earlier calculations, such that the renormalized interaction
term now becomes marginally stable rather than marginally unstable. We derive a
Ward identity and a renormalized form of the perturbation theory that
encompasses both the weak and strong coupling regimes and show that the
chi/gamma ratio is 8/3 (chi is the total susceptibility, spin plus isospin),
independent of the interaction U and in agreement with the NRG calculations.Comment: 23 pages, LaTeX, 11 figures includes as eps-files, submitted to Phys.
Rev.
Simple description of the anisotropic two-channel Kondo problem
We adapt strong-coupling methods first used in the one-channel Kondo model to
develop a simple description of the spin- two-channel Kondo model
with channel anisotropy. Our method exploits spin-charge decoupling to develop
a compactified Hamiltonian that describes the spin excitations. The structure
of the fixed-point Hamiltonian and quasiparticle impurity S-matrix are
incompatible with a Fermi liquid description.Comment: 4 pages, latex (uses revtex and epsf macros) with 3 figures - all in
a self unpacking uuencoded file. Revisions include changes to Fig. 1(a) and
detailed discussion of the spin excitation
Fostering the exchange of real world data across different countries to answer primary care research questions: an UNLOCK study from the IPCRG
There is growing awareness amongst healthcare planners, providers and researchers of the need to make better use of routinely collected health data by translating it into actionable information that improves efficiency of healthcare and patient outcomes. There is also increased acceptance of the importance of real world research that recruits patients representative of primary care populations and evaluates interventions realistically delivered by primary care professionals. The UNLOCK Group is an international collaboration of primary care researchers and practitioners from 15 countries. It has coordinated and shared datasets of diagnostic and prognostic variables for COPD and asthma to answer research questions meaningful to professionals working in primary care over a 6-year period. Over this time the UNLOCK Group has undertaken several studies using data from unselected primary care populations from diverse contexts to evaluate the burden of disease, multiple morbidities, treatment and follow-up. However, practical and structural constraints have hampered the UNLOCK Group's ability to translate research ideas into studies. This study explored the constraints, challenges and successes experienced by the UNLOCK Group and its participants' learning as researchers and primary care practitioners collaborating to answer primary care research questions. The study identified lessons for future studies and collaborations that require data sharing across borders. It also explored specific challenges to fostering the exchange of primary care data in comparison to other datasets such as public health, prescribing or hospital data and mechanisms that may be used to overcome these.The IPCRG provided funding for this research project as an UNLOCK Group study for which the funding was obtained through an unrestricted grant by Novartis AG, Basel, Switzerland. Novartis has no role in study design, data collection and analysis, decision to publish, or preparation of the manuscriptinfo:eu-repo/semantics/publishedVersio
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