12,050 research outputs found
Magnetic, thermal and transport properties of Cd doped CeIn
We have investigated the effect of Cd substitution on the archetypal heavy
fermion antiferromagnet CeIn via magnetic susceptibility, specific heat and
resistivity measurements. The suppression of the Neel temperature, T,
with Cd doping is more pronounced than with Sn. Nevertheless, a doping induced
quantum critical point does not appear to be achievable in this system. The
magnetic entropy at and the temperature of the maximum in resistivity are
also systematically suppressed with Cd, while the effective moment and the
Curie-Weiss temperature in the paramagnetic state are not affected. These
results suggest that Cd locally disrupts the AFM order on its neighboring Ce
moments, without affecting the valence of Ce. Moreover, the temperature
dependence of the specific heat below is not consistent with 3D magnons
in pure as well as in Cd-doped CeIn, a point that has been missed in
previous investigations of CeIn and that has bearing on the type of quantum
criticality in this system
Superconductivity without Fe or Ni in the phosphides BaIr2P2 and BaRh2P2
Heat capacity, resistivity, and magnetic susceptibility measurements confirm
bulk superconductivity in single crystals of BaIrP (T=2.1K) and
BaRhP (T = 1.0 K). These compounds form in the ThCrSi (122)
structure so they are isostructural to both the Ni and Fe pnictides but not
isoelectronic to either of them. This illustrates the importance of structure
for the occurrence of superconductivity in the 122 pnictides. Additionally, a
comparison between these and other ternary phosphide superconductors suggests
that the lack of interlayer bonding favors superconductivity. These
stoichiometric and ambient pressure superconductors offer an ideal playground
to investigate the role of structure for the mechanism of superconductivity in
the absence of magnetism.Comment: Published in Phys Rev B: Rapid Communication
Thermalization of a Brownian particle via coupling to low-dimensional chaos
It is shown that a paradigm of classical statistical mechanics --- the
thermalization of a Brownian particle --- has a low-dimensional, deterministic
analogue: when a heavy, slow system is coupled to fast deterministic chaos, the
resultant forces drive the slow degrees of freedom toward a state of
statistical equilibrium with the fast degrees. This illustrates how concepts
useful in statistical mechanics may apply in situations where low-dimensional
chaos exists.Comment: Revtex, 11 pages, no figures
Level spacings and periodic orbits
Starting from a semiclassical quantization condition based on the trace
formula, we derive a periodic-orbit formula for the distribution of spacings of
eigenvalues with k intermediate levels. Numerical tests verify the validity of
this representation for the nearest-neighbor level spacing (k=0). In a second
part, we present an asymptotic evaluation for large spacings, where consistency
with random matrix theory is achieved for large k. We also discuss the relation
with the method of Bogomolny and Keating [Phys. Rev. Lett. 77 (1996) 1472] for
two-point correlations.Comment: 4 pages, 2 figures; major revisions in the second part, range of
validity of asymptotic evaluation clarifie
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Materials for phantoms for terahertz pulsed imaging
Phantoms are commonly used in medical imaging for quality assurance, calibration, research and teaching. They may include test patterns or simulations of organs, but in either case a tissue substitute medium is an important component of the phantom. The aim of this work was to identify materials suitable for use as tissue substitutes for the relatively new medical imaging modality terahertz pulsed imaging. Samples of different concentrations of the candidate materials TX151 and napthol green dye were prepared, and measurements made of the frequency-dependent absorption coefficient (0.5 to 1.5 THz) and refractive index (0.5 to 1.0 THz). These results were compared qualitatively with measurements made in a similar way on samples of excised human tissue (skin, adipose tissue and striated muscle). Both materials would be suitable for phantoms where the dominant mechanism to be simulated is absorption (similar to ∼100 cm(-1) at 1 THz) and where simulation of the strength of reflections from boundaries is not important; for example, test patterns for spatial resolution measurements. Only TX151 had a frequency-dependent refractive index close to that of tissue, and could therefore be used to simulate the layered structure of skin, the complexity of microvasculature or to investigate frequency-dependent interference effects that have been noted in terahertz images
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