867 research outputs found
Expanding Semiflows on Branched Surfaces and One-Parameter Semigroups of Operators
We consider expanding semiflows on branched surfaces. The family of transfer
operators associated to the semiflow is a one-parameter semigroup of operators.
The transfer operators may also be viewed as an operator-valued function of
time and so, in the appropriate norm, we may consider the vector-valued Laplace
transform of this function. We obtain a spectral result on these operators and
relate this to the spectrum of the generator of this semigroup. Issues of
strong continuity of the semigroup are avoided. The main result is the
improvement to the machinery associated with studying semiflows as
one-parameter semigroups of operators and the study of the smoothness
properties of semiflows defined on branched manifolds, without encoding as a
suspension semiflow
Field-induced magnetic ordering in the Haldane system PbNi2V2O8
The Haldane system PbNi2V2O8 was investigated by the temperature dependent
magnetization M(T) measurements at fields higher than H_c, with H_c the
critical fields necessary to close the Haldane gap. It is revealed that M(T)
for H > H_c exhibits a cusp-like minimum at T_{min}, below which M(T) increases
with decreasing T having a convex curve. These features have been observed for
both and , with c-axis being parallel to the chain.
These data indicate the occurrence of field-induced magnetic ordering around
T_{min}. Phase boundaries for and do not cross each
other, consistent with the theoretical calculation for negative single-ion
anisotropy D.Comment: 3 figures, submitted to Phys. Rev.
Novel Quantum Criticality in CeRuSi near Absolute Zero Observed by Thermal Expansion and Magnetostriction
We report linear thermal expansion and magnetostriction measurements for
CeRuSi in magnetic fields up to 52.6 mT and at temperatures down to 1
mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior:
The linear thermal expansion coefficient and the magnetostriction coefficient
were proportional to the temperature and magnetic field, respectively. In
contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The
negative contribution of thermal expansion and magnetostriction suggests the
existence of an additional quantum critical point
Valence and Na content dependences of superconductivity in NaxCoO2.yH2O
Various samples of sodium cobalt oxyhydrate with relatively large amounts of
Na ions were synthesized by a modified soft-chemical process in which a
NaOH aqueous solution was added in the final step of the procedure. From these
samples, a superconducting phase diagram was determined for a section of a
cobalt valence of +3.48, which was compared with a previously obtained
one of +3.40. The superconductivity was significantly affected by the
isovalent exchanger of Na and HO, rather than by variation of
Co valence, suggesting the presence of multiple kinds of Fermi surface.
Furthermore, the high-field magnetic susceptibility measurements for one sample
up to 30 T indicated an upper critical field much higher than the Pauli limit
supporting the validity of the spin-triplet pairing mechanism.Comment: 4 figures and 1 tabl
Tomonaga-Luttinger Liquid in a Quasi-One-Dimensional S=1 Antiferromagnet Observed by the Specific Heat
Specific heat experiments on single crystals of the S=1 quasi-one-dimensional
bond-alternating antiferromagnet Ni(C_9H_24N_4)(NO_2)ClO_4, alias NTENP, have
been performed in magnetic fields applied both parallel and perpendicular to
the spin chains. We have found for the parallel field configuration that the
magnetic specific heat (C_mag) is proportional to temperature (T) above a
critical field H_c, at which the energy gap vanishes, in a temperature region
above that of the long-range ordered state. The ratio C_mag/T increases as the
magnetic field approaches H_c from above. The data are in good quantitative
agreement with the prediction of the c=1 conformal field theory in conjunction
with the velocity of the excitations calculated by a numerical diagonalization,
providing a conclusive evidence for a Tomonaga-Luttinger liquid.Comment: 4 pages, 4 postscript figure
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