2,198 research outputs found
Heavy fermion fluid in high magnetic fields: an infrared study of CeRuSb
We report a comprehensive infrared magneto-spectroscopy study of
CeRuSb compound revealing quasiparticles with heavy effective mass
m, with a detailed analysis of optical constants in fields up to 17 T. We
find that the applied magnetic field strongly affects the low energy
excitations in the system. In particular, the magnitude of m 70
m (m is the quasiparticle band mass) at 10 K is suppressed by as much
as 25 % at 17 T. This effect is in quantitative agreement with the mean-field
solution of the periodic Anderson model augmented with a Zeeman term
Effects of lattice distortion and Jahn–Teller coupling on the magnetoresistance of La0.7Ca0.3MnO3 and La0.5Ca0.5CoO3 epitaxial films
Studies of La0.7Ca0.3MnO3 epitaxial films on substrates with a range of lattice constants reveal two dominant contributions to the occurrence of colossal negative magnetoresistance (CMR) in these manganites: at high temperatures (T → TC, TC being the Curie temperature), the magnetotransport properties are predominantly determined by the conduction of lattice polarons, while at low temperatures (T ≪ TC/, the residual negative magnetoresistance is correlated with the substrate-induced lattice distortion which incurs excess magnetic domain wall scattering. The importance of lattice polaron conduction associated with the presence of Jahn–Teller coupling in the manganites is further verified by comparing the manganites with epitaxial films of another ferromagnetic perovskite, La0.5Ca0.5CoO3. Regardless of the differences in the substrate-induced lattice distortion, the cobaltite films exhibit much smaller negative magnetoresistance, which may be attributed to the absence of Jahn–Teller coupling and the high electron mobility that prevents the formation of lattice polarons. We therefore suggest that lattice polaron conduction associated with the Jahn–Teller coupling is essential for the occurrence of CMR, and that lattice distortion further enhances the CMR effects in the manganites
Ageing as developmental decay: insights from p16(INK4a.)
The p16(INK4a) cell cycle regulator is one of the best ageing biomarkers because it is suppressed in early embryogenesis and progressively induced during ageing. p16(INK4a) plays a crucial role in key cell fate decisions which contribute to ageing, such as cellular senescence and stem cell dynamics. Detailed examination of the pathways regulating p16(INK4a) expression has revealed an overlap with those regulating early development. We present the hypothesis that ageing might be primarily driven by gradual functional decay of developmental pathways. To support this, we summarise the role of p16(INK4a) in ageing and our current knowledge on p16(INK4a) regulation. The developmental decay hypothesis implies that the much-evidenced damage associated with all aspects of ageing might be secondary to such decay
Site dilution of quantum spins in the honeycomb lattice
We discuss the effect of site dilution on both the magnetization and the
density of states of quantum spins in the honeycomb lattice, described by the
antiferromagnetic Heisenberg spin-S model. For this purpose a real-space
Bogoliubov-Valatin transformation is used. In this work we show that for the
S>1/2 the system can be analyzed in terms of linear spin wave theory. For spin
S=1/2, however, the linear spin wave approximation breaks down. In this case,
we have studied the effect of dilution on the staggered magnetization using the
Stochastic Series Expansion Monte Carlo method. Two main results are to be
stressed from the Monte Carlo method: (i) a better value for the staggered
magnetization of the undiluted system, m=0.2677(6); (ii) a finite value of the
staggered magnetization of the percolating cluster at the classical percolation
threshold, showing that there is no quantum critical transition driven by
dilution in the Heisenberg model. In the solution of the problem using linear
the spin wave method we pay special attention to the presence of zero energy
modes. Using a combination of linear spin wave analysis and the recursion
method we were able to obtain the thermodynamic limit behavior of the density
of states for both the square and the honeycomb lattices. We have used both the
staggered magnetization and the density of states to analyze neutron scattering
experiments and Neel temperature measurements on quasi-two- -dimensional
honeycomb systems. Our results are in quantitative agreement with experimental
results on Mn_pZn_{1-p}PS_3 and on the Ba(Ni_pMg_{1-p})_2V_2O_8.Comment: 21 pages (REVTEX), 16 figure
Chiral magnetization textures stabilized by the Dzyaloshinskii-Moriya interaction during spin-orbit torque switching
We study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on
current-induced magnetic switching of a perpendicularly magnetized
heavy-metal/ferromagnet/oxide trilayer both experimentally and through
micromagnetic simulations. We report the generation of stable helical
magnetization stripes for a sufficiently large DMI strength in the switching
region, giving rise to intermediate states in the magnetization confirming the
essential role of the DMI on switching processes. We compare the simulation and
experimental results to a macrospin model, showing the need for a micromagnetic
approach. The influence of the temperature on the switching is also discussed.Comment: Includes corrected acknowledgements and clarification of simulation
parameter
Comorbidities of Idiopathic Thrombocytopenic Purpura: A Population-Based Study
A person experiencing more than one medical condition may have ambiguous clinical
presentation. ITP is a serious autoimmune disease with little epidemiological evidence on its
burden, risk factors, and comorbidities. Using the United Kingdom
general practice research database, we conducted a 14 years population-based
case control-type study to explore medical conditions more likely to cooccur with
ITP and their temporal relationship in association with ITP. ITP patients were matched
to non-ITP on practice, age, gender, and follow-up period. Potential comorbidities
were represented by patients' medical information at the preferred
term level of the MedDRA international classification. As well as death
(OR = 60.0; 95% CI [4.47–806.0]) and known clinical signs and symptoms
of ITP, ITP is associated with considerable number of medical conditions.
The association between ITP and some of these conditions is apparent both
before and after ITP diagnosis. Specific targeted studies can now be setup to reexamine
observed associations
Accurate Results from Perturbation Theory for Strongly Frustrated Heisenberg Spin Clusters
We investigate the use of perturbation theory in finite sized frustrated spin
systems by calculating the effect of quantum fluctuations on coherent states
derived from the classical ground state. We first calculate the ground and
first excited state wavefunctions as a function of applied field for a 12-site
system and compare with the results of exact diagonalization. We then apply the
technique to a 20-site system with the same three fold site coordination as the
12-site system. Frustration results in asymptotically convergent series for
both systems which are summed with Pad\'e approximants.
We find that at zero magnetic field the different connectivity of the two
systems leads to a triplet first excited state in the 12-site system and a
singlet first excited state in the 20-site system, while the ground state is a
singlet for both. We also show how the analytic structure of the Pad\'e
approximants at evolves in the complex plane at
the values of the applied field where the ground state switches between spin
sectors and how this is connected with the non-trivial dependence of the
number on the strength of quantum fluctuations. We discuss the origin
of this difference in the energy spectra and in the analytic structures. We
also characterize the ground and first excited states according to the values
of the various spin correlation functions.Comment: Final version, accepted for publication in Physical review
Subtlety of Determining the Critical Exponent of the Spin-1/2 Heisenberg Model with a Spatially Staggered Anisotropy on the Honeycomb Lattice
Puzzled by the indication of a new critical theory for the spin-1/2
Heisenberg model with a spatially staggered anisotropy on the square lattice as
suggested in \cite{Wenzel08}, we study a similar anisotropic spin-1/2
Heisenberg model on the honeycomb lattice. The critical point where the phase
transition occurs due to the dimerization as well as the critical exponent
are analyzed in great detail. Remarkly, using most of the available data
points in conjunction with the expected finite-size scaling ansatz with a
sub-leading correction indeed leads to a consistent with that
calculated in \cite{Wenzel08}. However by using the data with large number of
spins , we obtain which agrees with the most accurate Monte
Carlo O(3) value as well.Comment: 7 pages, 9 figures, 1 table, version accepted for publishin
Conductance through Quantum Dots Studied by Finite Temperature DMRG
With the Finite temperature Density Matrix Renormalization Group method
(FT-DMRG), we depeloped a method to calculate thermo-dynamical quantities and
the conductance of a quantum dot system. Conductance is written by the local
density of states on the dot. The density of states is calculated with the
numerical analytic continuation from the thermal Green's function which is
obtained directly from the FT-DMRG. Typical Kondo behaviors in the quantum dot
system are observed conveniently by comparing the conductance with the magnetic
and charge susceptibilities: Coulomb oscillation peaks and the unitarity limit.
We discuss advantage of this method compared with others.Comment: 14 pages, 13 fiure
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