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

Specific heat of the S=1S = 1 spin-dimer antiferromagnet Ba3_3Mn2_2O8_8 in high magnetic fields

We have measured the specific heat of the coupled spin-dimer antiferromagnet Ba$_3$Mn$_2$O$_8$ to 50 mK in temperature and to 29 T in the magnetic field. The experiment extends to the midpoint of the field region (25.9 T $\leq H \leq$ 32.3 T) of the magnetization plateau at 1/2 of the saturation magnetization, and reveals the presence of three ordered phases in the field region between that of the magnetization plateau and the low-field spin-liquid region. The exponent of the phase boundary with the thermally disordered region is smaller than the theoretical value based on the Bose-Einstein condensation of spin triplets. At zero field and 29 T, the specific-heat data show gapped behaviors characteristic of spin liquids. The zero-field data indicate that the gapped triplet excitations form two levels whose energies differ by nearly a factor of two. At least the lower level is well localized. The data at 29 T reveal that the low-lying excitations at the magnetization plateau are weakly delocalized.Comment: 6 pages, 5 figures, revised versio

Zeta functions and Dynamical Systems

In this brief note we present a very simple strategy to investigate dynamical determinants for uniformly hyperbolic systems. The construction builds on the recent introduction of suitable functional spaces which allow to transform simple heuristic arguments in rigorous ones. Although the results so obtained are not exactly optimal the straightforwardness of the argument makes it noticeable.Comment: 7 pages, no figuer

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 $H \parallel c$ and $H \perp c$, with c-axis being parallel to the chain. These data indicate the occurrence of field-induced magnetic ordering around T_{min}. Phase boundaries for $H \parallel c$ and $H \perp c$ do not cross each other, consistent with the theoretical calculation for negative single-ion anisotropy D.Comment: 3 figures, submitted to Phys. Rev.

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

Single crystal MgB2 with anisotropic superconducting properties

The discovery of superconductor in magnesium diboride MgB2 with high Tc (39 K) has raised some challenging issues; whether this new superconductor resembles a high temperature cuprate superconductor(HTS) or a low temperature metallic superconductor; which superconducting mechanism, a phonon- mediated BCS or a hole superconducting mechanism or other new exotic mechanism may account for this superconductivity; and how about its future for applications. In order to clarify the above questions, experiments using the single crystal sample are urgently required. Here we have first succeeded in obtaining the single crystal of this new MgB2 superconductivity, and performed its electrical resistance and magnetization measurements. Their experiments show that the electronic and magnetic properties depend on the crystallographic direction. Our results indicate that the single crystal MgB2 superconductor shows anisotropic superconducting properties and thus can provide scientific basis for the research of its superconducting mechanism and its applications.Comment: 7 pages pdf fil

Charged State of a Spherical Plasma in Vacuum

The stationary state of a spherically symmetric plasma configuration is investigated in the limit of immobile ions and weak collisions. Configurations with small radii are positively charged as a significant fraction of the electron population evaporates during the equilibration process, leaving behind an electron distribution function with an energy cutoff. Such charged plasma configurations are of interest for the study of Coulomb explosions and ion acceleration from small clusters irradiated by ultraintense laser pulses and for the investigation of ion bunches propagation in a plasma

Universality in heavy-fermion systems with general degeneracy

We discuss the relation between the T^{2}-coefficient of electrical resistivity $A$ and the T-linear specific-heat coefficient $\gamma$ for heavy-fermion systems with general $N$, where $N$ is the degeneracy of quasi-particles. A set of experimental data reveals that the Kadowaki-Woods relation; $A/\gamma^{2} = 1*10^{-5} {\mu\Omega}(K mol/mJ)^{2}$, collapses remarkably for large-N systems, although this relation has been regarded to be commonly applicable to the Fermi-liquids. Instead, based on the Fermi-liquid theory we propose a new relation; $\tilde{A}/\tilde{\gamma}^2=1\times10^{-5}$ with $\tilde{A} = A/(1/2)N(N-1)$ and $\tilde{\gamma} = \gamma/(1/2)N(N-1)$. This new relation exhibits an excellent agreement with the data for whole the range of degenerate heavy-fermions.Comment: 2 figures, to appear in Phys. Rev. Let