974 research outputs found
Optical absorption spectra in SrCu_2O_3 two-leg spin ladder
We calculate the phonon-assisted optical-absorption spectra in SrCu_2O_3
two-leg spin-ladder systems. The results for two models proposed for SrCu_2O_3
are compared. In the model including the effects of a cyclic four-spin
interaction, the shoulder structure appears at 978 cm^{-1} and the peak appears
at 1975 cm^{-1} in the spectrum for polarization of the electric field parallel
to the legs. In the other model which describes a pure two-leg ladder, the peak
appears around the lower edge of the spectrum at 1344 cm^{-1}. The feature can
be effective in determining the proper model for SrCu_2O_3.Comment: 5 pages, 5 figures, to appear in PRB vol. 67 (2003
Unusual behaviours and Impurity Effects in the Noncentrosymmetric Superconductor CePt3Si
We report a study in which the effect of defects/impurities, growth process,
off-stoichiometry, and presence of impurity phases on the superconducting
properties of noncentrosymmetric CePt3Si is analysed by means of the
temperature dependence of the magnetic penetration depth. We found that the
linear low-temperature response of the penetration depth -indicative of line
nodes in this material- is robust regarding sample quality, in contrast to what
is observed in unconventional centrosymmetric superconductors with line nodes.
We discuss evidence that the broadness of the superconducting transition may be
intrinsic, though not implying the existence of a second superconducting
transition. The superconducting transition temperature systematically occurs
around 0.75 K in our measurements, in agreement with resistivity and ac
magnetic susceptibility data but in conflict with specific heat, thermal
conductivity and NMR data in which Tc is about 0.5 K. Random defects do not
change the linear low-temperature dependence of the penetration depth in the
heavy-fermion CePt3Si with line nodes, as they do in unconventional
centrosymmetric superconductors with line nodes.Comment: To appear in New Journal of Physic
Regulation of Gâproteinâcoupled receptor kinase subtypes by calcium sensor proteins
Effective Crystalline Electric Field Potential in a j-j Coupling Scheme
We propose an effective model on the basis of a - coupling scheme to
describe local -electron states for realistic values of Coulomb interaction
and spin-orbit coupling , for future development of microscopic
theory of magnetism and superconductivity in -electron systems, where
is the number of local electrons. The effective model is systematically
constructed by including the effect of a crystalline electric field (CEF)
potential in the perturbation expansion in terms of . In this paper,
we collect all the terms up to the first order of . Solving the
effective model, we show the results of the CEF states for each case of
=25 with symmetry in comparison with those of the Stevens
Hamiltonian for the weak CEF. In particular, we carefully discuss the CEF
energy levels in an intermediate coupling region with in the order
of 0.1 corresponding to actual -electron materials between the and
- coupling schemes. Note that the relevant energy scale of is the
Hund's rule interaction. It is found that the CEF energy levels in the
intermediate coupling region can be quantitatively reproduced by our modified
- coupling scheme, when we correctly take into account the corrections in
the order of in addition to the CEF terms and Coulomb interactions
which remain in the limit of =. As an application of the
modified - coupling scheme, we discuss the CEF energy levels of filled
skutterudites with symmetry.Comment: 12 pages, 7 figures. Typeset with jpsj2.cl
Coexistence of magnetism and superconductivity in CeRh1-xIrxIn5
We report a thermodynamic and transport study of the phase diagram of
CeRh1-xIrxIn5. Superconductivity is observed over a broad range of doping, 0.3
< x < 1, including a substantial range of concentration (0.3 < x <0.6) over
which it coexists with magnetic order (which is observed for 0 < x < 0.6). The
anomalous transition to zero resistance that is observed in CeIrIn5 is robust
against Rh substitution. In fact, the observed bulk Tc in CeRh0.5Ir0.5In5 is
more than double that of CeIrIn5, whereas the zero-resistance transition
temperature is relatively unchanged for 0.5 < x < 1
Anisotropic three-dimentional magnetic fluctuations in heavy fermion CeRhIn5
CeRhIn5 is a heavy fermion antiferromagnet that orders at 3.8 K. The
observation of pressure-induced superconductivity in CeRhIn5 at a very high Tc
of 2.1 K for heavy fermion materials has led to speculations regarding to its
magnetic fluctuation spectrum. Using magnetic neutron scattering, we report
anisotropic three-dimensional antiferromagnetic fluctuations with an energy
scale of less than 1.7 meV for temperatures as high as 3Tc. In addition, the
effect of the magnetic fluctuations on electrical resistivity is well described
by the Born approximation.Comment: 4 pages, 4 figure
High-resolution x-ray study of the nematic - smectic-A and smectic-A - smectic-C transitions in 8barS5-aerosil gels
The effects of dispersed aerosil nanoparticles on two of the phase
transitions of the thermotropic liquid crystal material
4-n-pentylphenylthiol-4'-n-octyloxybenzoate 8barS5 have been studied using
high-resolution x-ray diffraction techniques. The aerosils hydrogen bond
together to form a gel which imposes a weak quenched disorder on the liquid
crystal. The smectic-A fluctuations are well characterized by a two-component
line shape representing thermal and random-field contributions. An elaboration
on this line shape is required to describe the fluctuations in the smectic-C
phase; specifically the effect of the tilt on the wave-vector dependence of the
thermal fluctuations must be explicitly taken into account. Both the magnitude
and the temperature dependence of the smectic-C tilt order parameter are
observed to be unaffected by the disorder. This may be a consequence of the
large bare smectic correlation length in the direction of modulation for this
transition. These results show that the understanding developed for the nematic
to smectic-A transition for octylcyanobiphenyl (8CB) and octyloxycyanobiphenyl
(8OCB) liquid crystals with quenched disorder can be extended to quite
different materials and transitions.Comment: 7 pages, 8 figure
High pressure phase diagrams of CeRhIn and CeCoIn studied by ac calorimetry
The pressure-temperature phase diagrams of the heavy fermion antiferromagnet
CeRhIn and the heavy fermion superconductor CeCoIn have been studied
under hydrostatic pressure by ac calorimetry and ac susceptibility measurements
using diamond anvil cells with argon as pressure medium. In CeRhIn, the use
of a highly hydrostatic pressure transmitting medium allows for a clean
simultaneous determination by a bulk probe of the antiferromagnetic and
superconducting transitions. We compare our new phase diagram with the previous
ones, discuss the nature (first or second order) of the various lines, and the
coexistence of antiferromagnetic order and superconductivity. The link between
the collaps of the superconducting heat anomaly and the broadening of the
antiferromagnetic transition points to an inhomogeneous appearence of
superconductivity below GPa. Homogeneous bulk
superconductivity is only observed above this critical pressure. We present a
detailed analysis of the influence of pressure inomogeneities on the specific
heat anomalies which emphasizes that the observed broadening of the transitions
near is connected with the first order transition. For CeCoIn we show
that the large specific heat anomaly observed at at ambient pressure is
suppressed linearly at least up to 3 GPa
phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism
It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperm
Spin relaxation of conduction electrons in bulk III-V semiconductors
Spin relaxation time of conduction electrons through the Elliot-Yafet,
D'yakonov-Perel and Bir-Aronov-Pikus mechanisms is calculated theoretically for
bulk GaAs, GaSb, InAs and InSb of both - and -type. Relative importance
of each spin relaxation mechanism is compared and the diagrams showing the
dominant mechanism are constructed as a function of temperature and impurity
concentrations. Our approach is based upon theoretical calculation of the
momentum relaxation rate and allows understanding of the interplay between
various factors affecting the spin relaxation over a broad range of temperature
and impurity concentration.Comment: an error in earlier version correcte
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