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

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

Anisotropic low field behavior and the observation of flux jumps in CeCoIn5

The magnetic behavior of the heavy fermion superconductor CeCoIn5 has been investigated. The low field magnetization data show flux jumps in the mixed state of the superconducting phase in a restricted range of temperature. These flux jumps begin to disappear below 1.7 K, and are completely absent at 1.5 K. The magnetization loops are asymmetric, suggesting that surface and geometrical factors dominate the pinning in this system. The lower critical field (Hc1), obtained from the magnetization data, shows a linear temperature dependence and is anisotropic. The calculated penetration depth is also anisotropic, which is consistent with the observation of an anisotropic superconducting gap in CeCoIn5. The critical currents, determined from the high field isothermal magnetization loops, are comparatively low (around 4000 A/cm2 at 1.6 K and 5 kOe).Comment: 4 pages 3 figure

High magnetic field phase diagram of PrOs4Sb12

The magnetic phase diagram of PrOs$_4$Sb$_{12}$ has been investigated by specific heat measurements between 8 and 32 T. A new Schottky anomaly due to excitations between two lowest crystalline-electric-field (CEF) singlets, has been found for both $H \parallel (100)$ and $H \parallel (110)$ above the field where the field-induced ordered phase (FIOP) is suppressed. The constructed $H-T$ phase diagram shows weak magnetic anisotropy and implies a crossing of the two CEF levels at about 8 - 9 T for both field directions. These results provide an unambiguous evidence for the $\Gamma_1$ singlet being the CEF ground state and suggest the level crossing (involving lowest CEF levels) as the driving mechanism of FIOP.Comment: Submitted to Phys. Rev. Let

On the origin of multiple ordered phases in PrFe4P12

The nature of multiple electronic orders in skutterudite PrFe_4P_{12} is discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction of \Gamma_3 symmetry. The high-field phase can be reproduced qualitatively provided (i) ferro-type interactions are introduced between the dipoles as well as between the octupoles of localized f-electrons, and (ii) separation is vanishingly small between the \Gamma_1-\Gamma_4^{(1)} crystalline electric field (CEF) levels. The high-field phase can have either the same ordering vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on the parameters. In the latter case, distortion of the crystal perpendicular to the (111) axis is predicted. The corresponding anomaly in elastic constants should also appear. The electrical resistivity is calculated with account of scattering within the CEF quasi-quartet. It is found that the resistivity as a function of the direction of magnetic field shows a sharp maximum around the (111) axis at low temperatures because of the level crossing.Comment: 16 pages, 5 figure

Microscopic Mechanism for Staggered Scalar Order in PrFe4P12

A microscopic model is proposed for the scalar order in PrFe4P12 where f2 crystalline electric field (CEF) singlet and triplet states interact with two conduction bands. By combining the dynamical mean-field theory and the continuous-time quantum Monte Carlo, we obtain an electronic order with staggered Kondo and CEF singlets with the total conduction number being unity per site. The ground state becomes semimetallic provided that the two conduction bands have different occupation numbers. This model naturally explains experimentally observed properties in the ordered phase of PrFe4P12 such as the scalar order parameter, temperature dependence of the resistivity, field-induced staggered moment, and inelastic features in neutron scattering. The Kondo effect plays an essential role for ordering, in strong contrast with ordinary magnetic orders by the RKKY interaction.Comment: 4 pages, 4figure

Evidence for Octupole Order in Ce0.7_{0.7}La0.3_{0.3}B6_6 from Resonant X-ray Scattering

The azimuthal angle dependence observed in the resonant X-ray scattering in phase IV of Ce$_{0.7}$La$_{0.3}$B$_6$ is analyzed theoretically. It is shown that the peculiar angle dependence observed in the E2 channel is consistent with the Gamma_{5u}-type octupole order with principal axis along (111) and equivalent directions. Under the assumption that the four equivalent octupole domains are nearly equally populated in the sample, the observed angle dependences are reproduced by calculation for both sigma-sigma' and sigma-pi' polarizations. The calculation for various symmetries of order parameters excludes unambiguously other order parameters than the Gamma_{5u}-type octupole.Comment: 4 pages, 2 figures, 3 tables, in JPSJ forma