Staggered Pairing Phenomenology for UPd_2Al_3 and UNi_2Al_3

We apply the staggered-pairing Ginzburg-Landau phenomenology to describe superconductivity in UPd_2Al_3 and UNi_2Al_3. The phenomenology was applied successfully to UPt_3 so it explains why these materials have qualitatively different superconducting phase diagrams although they have the same point-group symmetry. UPd_2Al_3 and UNi_2Al_3 have a two-component superconducting order parameter transforming as an H-point irreducible representation of the space group. Staggered superconductivity can induce charge-density waves characterized by new Bragg peaks suggesting experimental tests of the phenomenology.Comment: 4 pages, REVTeX, 2 Postscript figure

Surface superconductivity and order parameter suppression in UPt3_3

We show that a recent measurement of surface superconductivity in UPt$_3$ (Keller {\it et. al.}, Phys. Rev. Lett. {\bf 73}, 2364 (1994)) can be understood if the superconducting pair wavefunction is suppressed anisotropically at a vacuum to superconductor interface. Further measurements of surface superconductivity can distinguish between the various phenomenological models of superconducting UPt$_3$.Comment: 4 pages, latex, 2 Figures available upon request ([email protected]

Antiferromagnetic Domains and Superconductivity in UPt3

We explore the response of an unconventional superconductor to spatially inhomogeneous antiferromagnetism (SIAFM). Symmetry allows the superconducting order parameter in the E-representation models for UPt3 to couple directly to the AFM order parameter. The Ginzburg-Landau equations for coupled superconductivity and SIAFM are solved numerically for two possible SIAFM configurations: (I) abutting antiferromagnetic domains of uniform size, and (II) quenched random disorder of `nanodomains' in a uniform AFM background. We discuss the contributions to the free energy, specific heat, and order parameter for these models. Neither model provides a satisfactory account of experiment, but results from the two models differ significantly. Our results demonstrate that the response of an E_{2u} superconductor to SIAFM is strongly dependent on the spatial dependence of AFM order; no conclusion can be drawn regarding the compatibility of E_{2u} superconductivity with UPt3 that is independent of assumptions on the spatial dependence of AFMComment: 12 pages, 13 figures, to appear in Phys. Rev.

Superconductivity in heavy-fermion U(Pt,Pd)3 and its interplay with magnetism

The effect of Pd doping on the superconducting phase diagram of the unconventional superconductor UPt3 has been measured by (magneto)resistance, specific heat, thermal expansion and magnetostriction. Experiments on single- and polycrystalline U(Pt1-xPdx)3 for x<= 0.006 show that the superconducting transition temperatures of the A phase, Tc+, and of the B phase, Tc-, both decrease, while the splitting DTc increases at a rate of 0.30(2)K/at.%Pd. We find that DTc(x) correlates with an increase of the weak magnetic moment m(x) upon Pd doping. This provides further evidence for Ginzburg-Landau scenarios with magnetism as the symmetry breaking field, i.e. the 2D E representation and the 1D odd parity model. Only for small splittings DTc is proportional to m^2(Tc+) (DTc<= 0.05 K) as predicted. The results at larger splittings call for Ginzburg-Landau expansions beyond 4th order. The tetracritical point in the B-T plane persists till at least x= 0.002 for B perpendicular to c, while it is rapidly suppressed for B||c. Upon alloying the A and B phases gain stability at the expense of the C phase.Comment: 25 pages text (PS), 8 pages with 14 figures (PS), submitted to Phys.Rev.

E1gE_{1g} model of superconducting UPt3_3

The phase diagram of superconducting UPt$_3$ is explained in a Ginzburg-Landau theory starting from the hypothesis that the order parameter is a pseudo-spin singlet which transforms according to the $E_{1g}$ representation of the $D_{6h}$ point group. We show how to compute the positions of the phase boundaries both when the applied field is in the basal plane and when it is along the c-axis. The experimental phase diagrams as determined by longitudinal sound velocity data can be fit using a single set of parameters. In particular the crossing of the upper critical field curves for the two field directions and the apparent isotropy of the phase diagram are reproduced. The former is a result of the magnetic properties of UPt$_3$ and their contribution to the free energy in the superconducting state. The latter is a consequence of an approximate particle-hole symmetry. Finally we extend the theory to finite pressure and show that, in contrast to other models, the $E_{1g}$ model explains the observed pressure dependence of the phase boundaries.Comment: RevTex, 29 pages, 18 PostScript figures in a uuencoded, gzipped tar file. PostScript version of paper, tar file of PostScript figures and individual PostScript figures are also available via anonymous ftp at ftp://nym.physics.wisc.edu/anonymou/papers/upt3

Childhood leukaemia in Europe after Chernobyl: 5 year follow-up.

The European Childhood Leukaemia - Lymphoma Incidence Study (ECLIS) is designed to address concerns about a possible increase in the risk of cancer in Europe following the nuclear accident in Chernobyle in 1986. This paper reports results of surveillance of childhood leukaemia in cancer registry populations from 1980 up to the end of 1991. There was a slight increase in the incidence of childhood leukaemia in Europe during this period, but the overall geographical pattern of change bears no relation to estimated exposure to radiation resulting from the accident. We conclude that at this stage of follow-up any changes in incidence consequent upon the Chernobyl accident remain undetectable against the usual background rates. Our results are consistent with current estimates of the leukaemogenic risk of radiation exposure, which, outside the immediate vicinity of the accident, was small