Tree analysis code /TRACE/ program E64106. NERVA program

Computer program for Monte Carlo simulation of fault trees in analysis of large complex system

Metamagnetic Quantum Criticality Revealed by 17O-NMR in the Itinerant Metamagnet Sr3Ru2O7

We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7 as a function of magnetic field and temperature using 17O-NMR. This system sits close to a metamagnetic quantum critical point (MMQCP) for the field perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior at low temperatures except for a narrow field region close to the MMQCP. The nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced on approaching the metamagnetic critical field of 7.9 T and at the critical field 1/T1T continues to increase and does not show Fermi- liquid behavior down to 0.3 K. The temperature dependence of T1T in this region suggests the critical temperature Theta to be 0 K, which is a strong evidence that the spin dynamics possesses a quantum critical character. Comparison between uniform susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of two-dimensional ferromagnetic fluctuations dominate the spin fluctuation spectrum at the critical field, which is unexpected for itinerant metamagnetism.Comment: 5 pages, 4 figures, Accepted by Phys. Rev. Let

Antiferro-quadrupole state of orbital-degenerate Kondo lattice model with f^2 configuration

To clarify a key role of $f$ orbitals in the emergence of antiferro-quadrupole structure in PrPb$_{3}$, we investigate the ground-state property of an orbital-degenerate Kondo lattice model by numerical diagonalization techniques. In PrPb$_{3}$, Pr$^{3+}$ has a $4f^{2}$ configuration and the crystalline-electric-field ground state is a non-Kramers doublet $\Gamma_{3}$. In a $j$-$j$ coupling scheme, the $\Gamma_{3}$ state is described by two local singlets, each of which consists of two $f$ electrons with one in $\Gamma_{7}$ and another in $\Gamma_{8}$ orbitals. Since in a cubic structure, $\Gamma_{7}$ has localized nature, while $\Gamma_{8}$ orbitals are rather itinerant, we propose the orbital-degenerate Kondo lattice model for an effective Hamiltonian of PrPb$_{3}$. We show that an antiferro-orbital state is favored by the so-called double-exchange mechanism which is characteristic of multi-orbital systems.Comment: 3 pages, 3 figures, Proceedings of Skutterudite2007 (September 26-30, 2007, Kobe

Observation of a Liquid-Gas-Type Transition in the Pyrochlore Spin Ice Compound Dy2Ti2O7 in a Magnetic Field

Low temperature magnetization measurements on the pyrochlore spin ice compound Dy2Ti2O7 reveal that the ice-rule breaking spin flip, appearing at H∼0.9  T applied parallel to the [111] direction, turns into a novel first-order transition for T<0.36   K which is most probably of a liquid-gas type. T-linear variation of the critical field observed down to 0.03 K suggests the unusual situation that the entropy release across the transition remains finite [∼0.5   (J/K)⋅mol−Dy] as T→0, in accordance with a breaking of the macroscopic degeneracy in the intermediate “kagomé ice” state

Eastward traverse of equatorial plasma plumes observed with the Equatorial Atmosphere Radar in Indonesia

The zonal structure of radar backscatter plumes associated with Equatorial Spread F (ESF), probably modulated by atmospheric gravity waves, has been investigated with the Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20&amp;deg; S, 100.32&amp;deg; E; dip latitude 10.1&amp;deg; S) and the FM-CW ionospheric sounders on the same magnetic meridian as the EAR. The occurrence locations and zonal distances of the ESF plumes were determined with multi-beam observations with the EAR. The ESF plumes drifted eastward while keeping distances of several hundred to a thousand kilometers. Comparing the occurrence of the plumes and the F-layer uplift measured by the FM-CW sounders, plumes were initiated within the scanned area around sunset only, when the F-layer altitude rapidly increased. Therefore, the PreReversal Enhancement (PRE) is considered as having a zonal variation with the scales mentioned above, and this variation causes day-to-day variability, which has been studied for a long time. Modulation of the underlying E-region conductivity by gravity waves, which causes inhomogeneous sporadic-E layers, for example, is a likely mechanism to determine the scale of the PRE

Tuning Heavy Fermion Systems into Quantum Criticality by Magnetic Field

We discuss a series of thermodynamic, magnetic and electrical transport experiments on the two heavy fermion compounds CeNi2Ge2 and YbRh2Si2 in which magnetic fields, B, are used to tune the systems from a Non-Fermi liquid (NFL) into a field-induced FL state. Upon approaching the quantum-critical points from the FL side by reducing B we analyze the heavy quasiparticle (QP) mass and QP-QP scattering cross sections. For CeNi2Ge2 the observed behavior agrees well with the predictions of the spin-density wave (SDW) scenario for three-dimensional (3D) critical spin-fluctuations. By contrast, the observed singularity in YbRh2Si2 cannot be explained by the itinerant SDW theory for neither 3D nor 2D critical spinfluctuations. Furthermore, we investigate the magnetization M(B) at high magnetic fields. For CeNi2Ge2 a metamagnetic transition is observed at 43 T, whereas for YbRh2Si2 a kink-like anomaly occurs at 10 T in M vs B (applied along the easy basal plane) above which the heavy fermion state is completely suppressed.Comment: 15 pages, 8 figures, submitted to Journal of Low Temperature Physics, special Series on "High Magnetic Field Facilities

Anomalous Anisotropic Magnetoresistance in Heavy-Fermion PrFe4P12

We have investigated the anisotropy of the magnetoresistance in the Pr-based HF compound PrFe4P12. The large anisotropy of effective mass and its strong field dependence have been confirmed by resistivity measurements. Particularly for H||[111], where the effective mass is most strongly enhanced, the non-Fermi liquid behavior has been observed. Also, we have found the angular dependence of the magnetoresistance sharply enhanced at H||[111], which is evidently correlated with both the non-Fermi liquid behavior and the high-field ordered state (B-phase).Comment: 3 pages, 3 figures. J. Phys. Soc. Jpn. Vol.77, No.8, in pres

Theoretical Description of Nearly Discontinuous Transition in Superconductors with Paramagnetic Depairing

Based on a theoretical argument and Monte Carlo simulations of a Ginzburg-Landau model derived microscopically, it is argued that, in type-II superconductors where {\it both} the paramagnetic {\it and} orbital depairings are important, a strong first-order transition (FOT) at $H_{c2}$ expected in the mean field (MF) approximation never occurs in real systems and changes due to the fluctuation into a crossover. The present result explains why a {\it nearly} discontinuous crossover at $H_{c2}$ with {\it no} intrinsic hysteresis is observed only in a clean superconducting material with a singlet pairing and a high condensation energy such as CeCoIn$_5$.Comment: Publication version. See cond-mat/0306060 regarding a corresponding long pape