Showing papers by "M. B. Maple published in 2004"
TL;DR: The results of inelastic neutron scattering provide a solution for the crystal field level scheme in PrOs4Sb12, in which the ground state in the cubic crystal field potential of T(h) symmetry is a Gamma(1) singlet, and it is proposed that aspherical Coulomb scattering is responsible for enhancing the superconducting transition temperature.
Abstract: The results of inelastic neutron scattering provide a solution for the crystal field level scheme in PrOs4Sb12, in which the ground state in the cubic crystal field potential of T(h) symmetry is a Gamma(1) singlet. The conduction electron mass enhancement is consistent with inelastic exchange scattering, and we propose that inelastic quadrupolar, or aspherical Coulomb, scattering is responsible for enhancing the superconducting transition temperature. PrOs4Sb12 appears to be the first compound in which aspherical Coulomb scattering is strong enough to overcome magnetic pair breaking and increase T(c).
113 citations
TL;DR: In this paper, Cao et al. proposed a method to estimate the distance between two points of interest in a single image by using the distance from a single point of interest to the center of the image.
Abstract: D. Cao,1,3 F. Bridges,1 P. Chesler,1 S. Bushart,1 E. D. Bauer,2 and M. B. Maple2 1Physics Deparment, University of California, Santa Cruz, California 95064, USA 2Department of Physics and Institute of Pure and Applied Physical Science, University of California, San Diego, La Jolla, California 92093, USA 3MS K764, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA (Received 24 October 2003; revised manuscript received 8 July 2004; published 20 September 2004)
69 citations
TL;DR: In this paper, X-ray powder-diffraction, magnetic-susceptibility, and electrical resistivity measurements were made on single crystals of the filled skutterudite series.
Abstract: X-ray powder-diffraction, magnetic-susceptibility $\ensuremath{\chi}(T),$ and electrical resistivity $\ensuremath{\rho}(T)$ measurements were made on single crystals of the filled skutterudite series $\mathrm{Pr}({\mathrm{Os}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{)}_{4}{\mathrm{Sb}}_{12}.$ One end of the series $(x=0)$ is a heavy fermion superconductor with a superconducting critical temperature ${T}_{c}=1.85\mathrm{K},$ while the other end $(x=1)$ is a conventional superconductor with ${T}_{c}\ensuremath{\approx}1\mathrm{K}.$ The lattice constant a decreases approximately linearly with increasing Ru concentration x. As Ru (Os) is substituted for Os (Ru), ${T}_{c}$ decreases nearly linearly with substituent concentration and exhibits a minimum with a value of ${T}_{c}=0.75\mathrm{K}$ at $x=0.6,$ suggesting that the two types of superconductivity compete with one another. Crystalline electric field effects in ${\ensuremath{\chi}}_{\mathrm{dc}}(T)$ and $\ensuremath{\rho}(T)$ due to the splitting of the ${\mathrm{Pr}}^{3+}$ ninefold degenerate Hund's rule $J=4$ multiplet are observed throughout the series, with the splitting between the ground state and the first excited state increasing monotonically as x increases. The fits to the ${\ensuremath{\chi}}_{\mathrm{dc}}(T)$ and $\ensuremath{\rho}(T)$ data are consistent with a ${\ensuremath{\Gamma}}_{3}$ doublet ground state for all values of x, although reasonable fits can be obtained for a ${\ensuremath{\Gamma}}_{1}$ ground state for x values near the end member compounds $(x=0$ or $x=1).$
64 citations
TL;DR: The physical properties of single crystals of filled skutterudite compounds EuT4Sb12 (T = Fe, Ru, Os) have been investigated by means of x-ray diffraction, electrical resistivity, specific heat, magnetization, and xray absorption spectroscopy measurements as mentioned in this paper.
Abstract: The physical properties of single crystals of filled skutterudite compounds EuT4Sb12 (T = Fe, Ru, Os) have been investigated by means of x-ray diffraction, electrical resistivity, specific heat, magnetization, and x-ray absorption spectroscopy measurements. The Eu-based materials crystallize in the LaFe4P12-type structure (space group ). A small Eu deficiency is encountered for Eu0.95Fe4Sb12, while the homologous compounds, Eu1.0Ru4Sb12 and Eu1.0Os4Sb12, reveal full occupancy of the Eu site. Eu0.95Fe4Sb12 appears to exhibit either canted ferromagnetic or ferrimagnetic order at TC = 88 K whereas EuRu4Sb12 and EuOs4Sb12 are ferromagnets with Curie temperatures of TC = 4 and 9 K, respectively. X-ray absorption near edge spectroscopy measurements reveal a nearly divalent Eu electronic configuration for EuT4Sb12 (T = Fe, Ru, Os) with no significant change with T atom or temperature.
58 citations
TL;DR: The superconductivity of graphite-sulfur composites is highly anisotropic and associated with the graphite planes, and the superconducting state coexists with the ferromagnetic magnetism of pure graphite as mentioned in this paper.
Abstract: The superconductivity of graphite-sulfur composites is highly anisotropic and associated with the graphite planes. The superconducting state coexists with the ferromagnetism of pure graphite, and a continuous crossover from superconducting to ferromagneticlike behavior could be achieved by increasing the magnetic field or the temperature. The angular dependence of the magnetic moment $m(\ensuremath{\alpha})$ provides evidence for an interaction between the ferromagnetic and the superconducting order parameters.
30 citations
TL;DR: In this article, a strong empirical correlation is established between electronic disorder and slow spin fluctuations in NFL materials, which suggest cooperative and critical spin fluctuations rather than a distribution of local fluctuation rates.
Abstract: Muon spin rotation and relaxation (μSR) experiments have yielded evidence that structural disorder is an important factor in many f-electron-based non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour are suggested by the observed broad and strongly temperature-dependent μSR (and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven theories (Kondo disorder, Griffiths–McCoy singularity) are, however, not capable of describing the time-field scaling seen in muon spin relaxation experiments, which suggest cooperative and critical spin fluctuations rather than a distribution of local fluctuation rates. A strong empirical correlation is established between electronic disorder and slow spin fluctuations in NFL materials.
29 citations
26 citations
TL;DR: In-plane angular magnetoresistivity Deltarho(anis)(ab)(theta) measurements were made on Y(1-x)Pr(x)Ba(2)Cu(3)O(7-delta) single crystals in the pseudogap region, indicating the presence of vortexlike excitations above the zero-field critical temperature in the Pseudo-Gap region.
Abstract: In-plane angular magnetoresistivity $\ensuremath{\Delta}{\ensuremath{\rho}}_{ab}^{\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{s}}$ measurements were made on ${\mathrm{Y}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{r}}_{x}\mathrm{B}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{u}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ single crystals in the pseudogap region For $x\ensuremath{\ge}02$ single crystals, $\ensuremath{\Delta}{\ensuremath{\rho}}_{ab}^{\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{s}}(\ensuremath{\theta})$ displays a deviation from the typical quasiparticle contribution ($\ensuremath{\propto}{sin }^{2}\ensuremath{\theta}$) for temperatures smaller than a certain value ${T}_{\ensuremath{\phi}}$ in the pseudogap region This deviation is consistent with a flux-flow type contribution to angular magnetoresistivity, indicating the presence of vortexlike excitations above the zero-field critical temperature in the pseudogap region
25 citations
TL;DR: In this article, the authors investigated the electronic structure, magnetic properties, and electrical resistivity of the Heusler alloys and reported x-ray photoelectron valence-band spectra and compared the results with those obtained from the selfconsistent tight-binding linearized muffin-tin orbital method.
Abstract: The aim of this work is to investigate electronic structure, magnetic properties, and electrical resistivity of the ${\mathrm{Fe}}_{2}{\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Sn}$ Heusler alloys. We report x-ray photoelectron valence-band spectra and compare the results with those obtained from the self-consistent tight-binding linearized muffin-tin orbital method. The changes in electronic and magnetic structure of the ${\mathrm{Fe}}_{2}{\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Sn}$ alloys were also investigated by means of the Korringa-Kohn-Rostocker Green's-function method in the coherent potential approximation. Numerical calculations yield the magnetic ground state for the ${\mathrm{Fe}}_{2}{\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Sn}$ alloys, when $xg~0.2$ in agreement with Slater-Pauling behavior. The band-structure calculations give a narrow peak in the density of states located in the energy gap near the Fermi level which is attributed to Fe antisite defects. The numerical calculations are in agreement with the experimental results recently obtained from infrared investigations of ${\mathrm{Fe}}_{2}\mathrm{TiSn}.$ We also report electrical resistivity calculations using a Falicov-Kimball model. Many-body calculations have shown that the narrow d band originating from the Fe impurity atoms is responsible for the unusual temperature dependencies of the physical properties of the ${\mathrm{Fe}}_{2}{\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}\mathrm{Sn}$ alloys.
23 citations
TL;DR: In this article, the infrared studies of the interlayer response for a series of YBa 2 Cu 3 O x high-T c superconductors with Pr, Ni, and Zn dopants, as well as for the optimally doped crystals of Bi 2 Sr 2 CaCu 2 O z.
Abstract: We report on the infrared studies of the interlayer response for a series of YBa 2 Cu 3 O x high-T c superconductors with Pr, Ni, and Zn dopants, as well as for the optimally doped crystals of Bi 2 Sr 2 CaCu 2 O z . These experimental results have motivated us to reexamine some of the long-standing issues in the interlayer electrodynamics of cuprates. Among them are the origins of the anomalous resonance specific to the conductivity of materials with more than one CuO 2 plane per unit cell, as well as the microscopic roots of the notorious "semiconducting" behavior seen in a variety of cuprates. Our data for Pr y Y 1 - y Ba 2 Cu 3 O 7 - δ samples indicate that the suppression of the superfluid density (and normal-state conductivity) with Y→Pr substitution occurs primarily due to changes in the electronic state of CuO 2 planes and not because of the fragmentation of Cu-O chains. We also show that the transverse Josephson plasma model proposed to explain the anomalous mode in the interlayer response is not fully consistent with the totality of the experimental data for double-layered materials. We discuss alternative/complimentary scenario assigning this feature of the c-axis conductivity to lifted degeneracy between bonding and antibonding bands associated with the two constituents of the CuO 2 bilayer (a so-called bilayer splitting effect).
15 citations
TL;DR: In this article, the intercalation of carbon nanotubes (CNs) in polycrystalline Bi2Sr2CaCu2O8 (BSCCO) samples at the 12 wt.%-CN doping level, based on high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction measurements was presented.
Abstract: Experimental evidence is presented for the intercalation of carbon nanotubes (CNs) in polycrystalline Bi2Sr2CaCu2O8 (BSCCO) samples at the 12 wt.%-CN doping level, based on high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction measurements. Magnetization measurements performed on BSCCO samples with various CN doping levels do not indicate a change in the critical current density Jc within experimental error. The embedding process did not have any detrimental effects on the superconducting critical temperature of any of the samples. In contrast to previous work, the temperatures and widths of the superconducting transition of all the samples were similar.
TL;DR: The existence of localized superconducting domains at elevated temperatures has been demonstrated for both pure graphite and graphite-sulfur composites as discussed by the authors, and the results of magnetization and magnetoresistance measurements provide further evidence for the local high-temperature superconductivity occurrence in these materials.
Abstract: Recently, the existence of localized superconducting domains at elevated temperatures has been demonstrated for both pure graphite and graphite–sulfur composites. In this note we report results of magnetization and magnetoresistance measurements which provide a further evidence for the local high-temperature superconductivity occurrence in these materials.
TL;DR: In this paper, the authors measured the temperature T dependence of the electrical resistivity ρ, specific heat C and magnetic susceptibility χ on the compound CeRhSn from about 10 K to temperatures as low as 0.1
Abstract: Measurements of the temperature T dependence of the electrical resistivity ρ, specific heat C and magnetic susceptibility χ have been made on the compound CeRhSn from about 10 K to temperatures as low as 0.1 K. Over certain temperature intervals, these properties are observed to have non-Fermi-liquid (NFL) temperature T dependences: with and . While the NFL behaviour can be described by the Griffiths–McCoy model, it may also be related to a weak magnetic transition at 6.2 K that depends on atomic disorder. The resistively determined upper critical field versus temperature curve of the isostructural reference compound without f electrons, LaRhSn, is also reported.
TL;DR: In this paper, the role of disorder in the non-Fermi-liquid behavior of the heavy-fermion alloys has been studied and the theoretical line shape is calculated from disorder-driven models and shows the same essential features as the observed spectra.
Abstract: The magnetic susceptibility and nuclear magnetic resonance $(\mathrm{NMR})$ linewidth have been measured in the heavy-fermion alloys ${\mathrm{CePtSi}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$, $x=0$ and $0.1$, to study the role of disorder in the non-Fermi-liquid $(\mathrm{NFL})$ behavior of this system. The theoretical $\mathrm{NMR}$ line shape is calculated from disorder-driven $\mathrm{NFL}$ models and shows the same essential features as the observed spectra. Analysis of $^{29}\mathrm{Si}$ and $^{195}\mathrm{Pt}$ $\mathrm{NMR}$ linewidths strongly suggests the existence of locally inhomogeneous susceptibility in both materials, and agrees with the widths of the local susceptibility distributions estimated from the susceptibility fits to the disorder-driven $\mathrm{NFL}$ models. Disorder-driven mechanisms can also explain the $\mathrm{NFL}$ behavior in ${\mathrm{CePtSi}}_{0.9}{\mathrm{Ge}}_{0.1}$; the $\mathrm{NMR}$ spectra do not, however, distinguish between the Kondo-disorder and Griffiths phase models. We find that stoichiometric $\mathrm{CePtSi}$ and $\mathrm{Ge}$-doped ${\mathrm{CePtSi}}_{0.9}{\mathrm{Ge}}_{0.1}$ show similar degrees of magnetic disorder, although a narrower distribution of local susceptibilities in $\mathrm{CePtSi}$ allows Fermi-liquid behavior to appear below $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The residual resistivity reported in $\mathrm{CePtSi}$ is relatively large, which indicates a significant level of intrinsic lattice defects and seems to be consistent with the disorder observed in the $\mathrm{NMR}$ spectra.
TL;DR: In this article, the pseudogap region of Y 1− x Pr x Ba 2 Cu 3 O 7− δ (x = 0, 0.42) single crystals reveal two regimes for the x ⩾0.20 samples, with a crossover at a temperature T c T T T cr.
Abstract: Magnetotransport measurements of Y 1− x Pr x Ba 2 Cu 3 O 7− δ ( x =0, 0.13, 0.2, 0.32, and 0.42) single crystals reveal two regimes in the pseudogap region for the x ⩾0.20 samples, with a crossover at a temperature T cr ( x ). For T c T T cr , there is a vortex-like response in magnetoresistivity. For T > T cr , the results are consistent with the picture in which the origin of the pseudogap is the nearly antiferromagnetic Fermi liquid renormalized by strong superconducting fluctuations.
TL;DR: In this article, the nuclear spin-lattice relaxation rate of the nuclear quadrupole resonance measurements on CeCoIn 5 under high pressure P was analyzed and it was shown that the value of 1/T 1 decreases rapidly with increasing P, reflecting that P moves CeCoin 5 away from the antiferromagnetic instability.
TL;DR: In this article, the results of 115In nuclear quadrupole resonance (NQR) measurements on Y-and La-substituted systems were reported, where the observed NQR frequency at an In(1) site varies linearly with lattice parameter and dopant concentration for Y- and Lasubstitized systems, which are expected to be from non-Fermi-liquid behavior near a quantum critical point.
Abstract: The results of 115In nuclear quadrupole resonance (NQR) measurements on Ce1−xYxRhIn5 and Ce1−xLaxRhIn5 are reported. The observed NQR frequency at an In(1) site varies linearly with lattice parameter and dopant concentration for Y- and La-substituted systems. For the samples of LaMIn5 (M=Co,Rh,Ir) and YRhIn5, T1−1’s are proportional to the temperature, which means the system is in the Fermi liquid state in a wide temperature range. On the other hand, in Ce0.1La0.9RhIn5 and Ce0.5Y0.5RhIn5, T1−1’s have power-law temperature dependences (close to T1/4), which are expected to be from non-Fermi-liquid behavior near a quantum critical point. For Ce0.5La0.5RhIn5 and Ce0.25La0.75RhIn5, T1−1’s stay temperature independent below 4.2 K and the observed linewidths of 115In become broader with decreasing temperature. This behavior may be associated with a short-range magnetic order of Ce expected from the macroscopic measurements.
TL;DR: In this article, a strong empirical correlation is established between electronic disorder and slow spin fluctuations in non-Fermi-liquid (NFL) materials, which suggest cooperative and critical spin fluctuations rather than a distribution of local fluctuation rates.
Abstract: Muon spin rotation and relaxation ($\mu$SR) experiments have yielded evidence that structural disorder is an important factor in many f-electron-based non-Fermi-liquid (NFL) systems. Disorder-driven mechanisms for NFL behaviour are suggested by the observed broad and strongly temperature-dependent $\mu$SR (and NMR) linewidths in several NFL compounds and alloys. Local disorder-driven theories (Kondo disorder, Griffiths-McCoy singularity) are, however, not capable of describing the time-field scaling seen in muon spin relaxation experiments, which suggest cooperative and critical spin fluctuations rather than a distribution of local fluctuation rates. A strong empirical correlation is established between electronic disorder and slow spin fluctuations in NFL materials