3,564 research outputs found
Evolution of Magnetism in Single-Crystal Honeycomb Iridates
We report the successful synthesis of single-crystals of the layered iridate,
(NaLi)IrO, , and a thorough study of
its structural, magnetic, thermal and transport properties. The new compound
allows a controlled interpolation between NaIrO and LiIrO,
while maintaing the novel quantum magnetism of the honeycomb Ir planes.
The measured phase diagram demonstrates a dramatic suppression of the N\'eel
temperature, , at intermediate suggesting that the magnetic order in
NaIrO and LiIrO are distinct, and that at , the
compound is close to a magnetically disordered phase that has been sought after
in NaIrO and LiIrO. By analyzing our magnetic data with a
simple theoretical model we also show that the trigonal splitting, on the
Ir ions changes sign from NaIrO and LiIrO, and the
honeycomb iridates are in the strong spin-orbit coupling regime, controlled by
\jeff=1/2 moments.Comment: updated version with more dat
Electric Dipolar Susceptibility of the Anderson-Holstein Model
The temperature dependence of electric dipolar susceptibility \chi_P is
discussed on the basis of the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) technique. Note that P is related with
phonon Green's function D. In order to obtain correct temperature dependence of
P at low temperatures, we propose a method to evaluate P through the Dyson
equation from charge susceptibility \chi_c calculated by the NRG, in contrast
to the direct NRG calculation of D. We find that the irreducible charge
susceptibility estimated from \chi_c agree with the perturbation calculation,
suggesting that our method works well.Comment: 4 pages, 4 figure
Kondo Effect in Fermi Systems with a Gap: A Renormalization Group Study
We present the results of a Wilson Renormalization Group study of the
single-impurity Kondo and Anderson models in a system with a gap in the
conduction electron spectrum. The behavior of the impurity susceptibility and
the zero-frequency response function, are discussed in the
cases with and without particle-hole symmetry. In addition, for the asymmetric
Anderson model the correlation functions, , are computed.Comment: 10 pages, 10 figure
Analytical results for random walks in the presence of disorder and traps
In this paper, we study the dynamics of a random walker diffusing on a
disordered one-dimensional lattice with random trappings. The distribution of
escape probabilities is computed exactly for any strength of the disorder.
These probabilities do not display any multifractal properties contrary to
previous numerical claims. The explanation for this apparent multifractal
behavior is given, and our conclusion are supported by numerical calculations.
These exact results are exploited to compute the large time asymptotics of the
survival probability (or the density) which is found to decay as . An exact lower bound for the density is found to
decay in a similar way.Comment: 21 pages including 3 PS figures. Submitted to Phys. Rev.
Prevalence of thyroid dysfunction and its association with controlled and uncontrolled type 2 diabetes mellitus in northern Andhra Pradesh population: a retrospective study
Background: The two important endocrinopathies, diabetes mellitus and thyroid dysfunction are interrelated to each other where the correlation is poorly understood. The thyroid dysfunction is more frequent in diabetics than general population. The present study was aimed to know the prevalence of thyroid dysfunction in type 2 diabetes mellitus (T2DM) and its association with controlled and uncontrolled T2DM.Methods: A retrospective study of 600 T2DM patients between 13-60 years of age with known thyroid status were included and the following parameters were examined: age, sex, body mass index (BMI), fasting blood sugar (FBS), HbA1C, free triiodothyronine (fT3), free tetraiodothyronine (fT4) and thyroid stimulating hormone (TSH).Results: The prevalence of thyroid dysfunction in T2DM patients was found to be 26.5% whereas 9% in healthy controls. Significantly elevated levels of FBS, HbA1C and TSH were observed whereas the levels of fT3, fT4 were found to be low in patients when compared to controls. Subclinical hypothyroidism (SCH) in diabetics (both controlled and uncontrolled) was more prevalent (15%) than it was found in healthy controls (5%). Similarly, overt hypothyroidism was also found to be high in diabetic patients (6%) as compared to healthy controls (2%). Significant difference (p <0.05) in the levels of TSH was found between group I (Controlled T2DM) and II (uncontrolled T2DM patients), also between groups II and III (Controls). Group II patients were found to have significant low levels of fT3 as compared to other two groups (Group I and III) (p<0.005).Conclusions: As SCH is more frequent in T2DM diabetes mellitus and untreated SCH patients have higher rate of complications, periodical screening is advised for thyroid dysfunction to prevent micro vascular and cardiovascular complications
Effect of Anharmonicity on the Kondo Phenomena of a Magnetic Ion Vibrating in a Confinement Potential
Effect of anharmonicity of a cage potential for a magnetic ion vibrating in a
metal is investigated by the numerical renormalization group method. The cage
potential is assumed to be one-dimensional and of the double-well type. In the
absence of the Coulomb interaction, we find continuous crossover among the
three limiting cases: Yu-Anderson-type Kondo regime, the double-well-type Kondo
one, and the renormalized Fermi chain one. In the entire parameter space of the
double-well potential, the ground state is described by a local Fermi liquid.
In the Yu-Anderson-type Kondo regime, a quantum phase transition to the ground
state with odd parity takes place passing through the two-channel Kondo fixed
point when the Coulomb interaction increases. Therefore, the vibration of a
magnetic ion in an oversized cage structure is a promising route to the
two-channel Kondo effect.Comment: 6 pages, 3 figures, accepted for JPS
First results from the CAWSES-India Tidal Campaign
The first CAWSES-India Tidal Campaign was conducted by the Indian scientific community during March–April 2006. The objectives of this campaign were: (1) To determine the characteristics of tides in the troposphere and lower stratosphere (0–20 km) and mesosphere and lower thermosphere (MLT) region (80–100 km), (2) to explore and identify what lower atmospheric processes drive middle atmospheric tides in the Indian continental region and (3) to provide information on those short-term variabilities of MLT tides that are likely to have an impact on the ionospheric variabilities and contribute to the upper atmospheric weather. Data sets from experiments conducted at the three low latitude radar sites, namely, Trivandrum (8.5&deg; N, 76.9&deg; E), Tirunelveli (8.7&deg; N, 77.8&deg; E) and Gadanki (13.5&deg; N, 79.2&deg; E) and fortnightly rocket launches from Thumba were made use of in this study. An important observational finding reported in this work is that the radar observations at Tirunelveli/Trivandrum indicate the presence of 15–20 day modulation of diurnal tide activity at MLT heights during the February–March period. A similar variation in the OLR fields in the western Pacific (120–160&deg; longitude region) suggests a possible link between the observed tidal variabilities and the variations in the deep tropical convection through the nonmigrating tides it generates
Quasiparticle Interactions for f-Impurity Anderson Model with Crystalline-Electric-Field: Numerical Renormalization Group Study
The aspect of the quasiparticle interaction of a local Fermi liquid, the
impurity version of f-based heavy fermions, is studied by the Wilson
numerical renormalization group method. In particular, the case of the
f-singlet crystalline-electric-field ground state is investigated assuming
the case of UPt with the hexagonal symmetry. It is found that the
interorbital interaction becomes larger than the intraorbital one in contrast
to the case of the bare Coulomb interaction for the parameters relevant to
UPt. This result offers us a basis to construct a microscopic theory of the
superconductivity of UPt where the interorbital interactions are expected
to play important roles.Comment: 9 pages, 5 figure
Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon
We discuss Kondo behavior of a conduction electron system coupled with local
optical phonon by analyzing the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) method. There appear three typical
regions due to the balance between Coulomb interaction and
phonon-mediated attraction . For , we
observe the standard Kondo effect concerning spin degree of freedom. Since the
Coulomb interaction is effectively reduced as , the
Kondo temperature is increased when is increased. On
the other hand, for , there occurs the Kondo effect
concerning charge degree of freedom, since vacant and double occupied states
play roles of pseudo-spins. Note that in this case, is decreased
with the increase of . Namely, should be maximized for
. Then, we analyze in detail the Kondo behavior
at , which is found to be explained by the polaron
Anderson model with reduced hybridization of polaron and residual repulsive
interaction among polarons. By comparing the NRG results of the polaron
Anderson model with those of the original Anderson-Holstein model, we clarify
the Kondo behavior in the competing region of .Comment: 8 pages, 8 figure
Wilson-like real-space renormalization group and low-energy effective spectrum of the XXZ chain in the critical regime
We present a novel real-space renormalization group(RG) for the
one-dimensional XXZ model in the critical regime, reconsidering the role of the
cut-off parameter in Wilson's RG for the Kondo impurity problem. We then
demonstrate the RG calculation for the XXZ chain with the free boundary.
Comparing the hierarchical structure of the obtained low-energy spectrum with
the Bethe ansatz result, we find that the proper scaling dimension is
reproduced as a fixed point of the RG transformation.Comment: 4 pages, 6 figures, typos corrected, final versio
- …