Showing papers by "M. B. Maple published in 1986"

Partially gapped Fermi surface in the heavy-electron superconductor URu2Si2.

Abstract: Transport, thermal, and magnetic data for the heavy electron system ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$ indicate that a charge- or spin-density-wave transition opens an energy gap of \ensuremath{\sim}11 meV over a portion of the Fermi surface below ${\mathrm{T}}_{0}$\ensuremath{\approxeq}17.5 K and demonstrate that bulk superconductivity occurs below ${\mathrm{T}}_{\mathrm{c}}$\ensuremath{\approxeq}1.5 K. The pressure dependences of ${\mathrm{T}}_{0}$ and ${\mathrm{T}}_{\mathrm{c}}$ support this interpretation. The unusually large initial slope of the upper critical magnetic field (9.2 T/K) is consistent with the high values of the electronic-specific-heat coefficient and the electrical resistivity.

Electronic structure of cerium and light rare-earth intermetallics

Abstract: We give an overview of the use of the impurity Anderson Hamiltonian to describe the spectroscopic and low-energy thermodynamic properties of cerium intermetallics, with emphasis on interpreting 4f photoemission spectra. We show Ce valence-band resonant photoemission, Bremsstrahlung isochromat and 3d X-ray photoemission spectra for CeRu2, CeNi2, CeIr2 and CeAl, and give a complete theoretical analysis of the spectra. We summarize the relation between the large and small energy scale properties. For each system, all the spectra, as well as the static magnetic susceptibility and Kondo temperature, can be described by the model using essentially the same parameters. We also present details of resonant photoemission spectra for five other cerium compounds, CeSi2, CeOs2, CePd3, CeCo2 and CeNi5, and discuss generally the problem of obtaining the experimental 4f spectrum. Alternative theories of 4f photoemission are examined critically and we give applications of the Anderson Hamiltonian theory to CeAl2,...

Superconductivity under pressure in (U1-xThx)Be13: Evidence for two superconducting states.

Abstract: The influence of pressure P on the superconducting transition temperature T/sub c/ has been determined for the (U/sub 1-//sub x/Th/sub x/)Be/sub 13/ system The magnitude of dT/sub c//dP increases by a factor of 3 for x>17% where an increase of T/sub c/ is observed at ambient pressure The phase diagram of T/sub c/(x) for P = 10 kbar shows two distinct regions of superconductivity

Novel Types of Superconductivity in F‐Electron Systems

Abstract: During the last one and one‐half decades, experiments on compounds and alloys of rare earth and actinide elements with partially filled f‐electron shells have revealed novel superconducting phenomena. Among these are the reappearance of resistance at a second critical temperature due to the interaction of magnetic moments with conduction electrons, the coexistence of superconductivity and antiferromagnetism, superconductivity induced by magnetic fields and superconductivity due to electrons with large effective masses.

Superconductivity and magnetic interactions in Yb 1.2−x Eu x Mo 6 S 8 pseudoternary compounds

Abstract: The superconducting and magnetic properties of the Yb /SUB 1.2-x/ Eu /SUB x/ Mo/sub 6/S/sub 8/ series of compounds have been investigated by means of ac magnetic susceptibility, electrical resistivity, and upper critical magnetic field H /SUB c2/ measurements. The superconducting transition temperature at ambient pressure is depressed by Eu additions, until superconductivity disappears completely at x about0.7. For Eu concentrations x<0.45, H /SUB c2/ is enhanced at low temperatures and exceeds the values for pure Yb /SUB 1.2/ Mo/sub 6/S/sub 8/. The temperature dependence of H /SUB c2/ for the various Yb /SUB 1.2-x/ Eu /SUB x/ Mo/sub 6/S/sub 8/ compounds is analyzed using a multiple pair-breaking theory that includes the compensation of the applied magnetic field by the negative exchange field produced by antiferromagnetic interactions between the conduction electron spins and the Eu/sup 2 +/ spins (Jaccarino-Peter effect). Hydrostatic pressure was found to induce superconductivity in all Eu-rich compositions that were not superconducting at ambient pressure.

Superconductivity, crystal-field effects, and magnetic order in the (Sm1-xYx)Rh4B4 mixed ternary system.

Abstract: The phase diagram of the superconducting transition temperature T/sub c/ and the magnetic ordering temperature T/sub M/ versus the composition x has been determined for the mixed ternary system (Sm/sub 1-x/Y/sub x/)Rh/sub 4/B/sub 4/. The x dependence of T/sub c/ is described well by the Abrikosov-Gor'kov theory modified to include the influence of the crystalline electric field on the Sm/sup 3 +/ ions. Heat-capacity measurements show that T/sub M/ decreases linearly with x at the rate dT/sub M//dx = -0.0128 K/(at. % Y). The influence of this magnetic order on superconductivity suggests that a transition from antiferromagnetism to ferromagnetism takes place for xapprox.0.4.

Properties of Niobium Recovered from Megabar Dynamic Pressures

Abstract: Nb was processed and recovered intact from peak dynamic pressures in the range 0.6–1.2 Mbar. Pressure and effective-plastic-strain histories were calculated using a finite-element hydrodynamic computer code. Recovered specimens were characterized by X-ray diffraction, metallography, Vicker’s hardness, and superconducting transition temperature Tc. The maximum change observed in the Tc of 9.18 K for the unshocked specimen was a decrease of 0.035 K in the specimen shocked to a maximum pressure of 0.6 Mbar. Shock processing of V3Si at 1 Mbar was recently reported by Stewart et al. to depress Tc 1.8 K from the initial value of 16.4 K. These results indicate that shock-induced defects and disorder have a relatively weak effect on the Tc of equilibrium phases and suggest that shock-synthesized metastable superconductors might have Tc’s close to intrinsic values for the ordered material.