Benoit Lussier

Universal Heat Conduction in YBa{sub 2}Cu{sub 3}O{sub 6.9}

The thermal conductivity of YBa{sub 2}Cu {sub 3}O{sub 6.9} was measured at low temperatures in untwinned single crystals with concentrations of Zn impurities from 0{percent} to 3{percent} of Cu. A linear term {kappa}{sub 0}/T=0.19mW K{sup {minus}2}cm{sup {minus}1} is clearly resolved as T{r_arrow}0, and found to be virtually independent of Zn concentration. The existence of this residual normal fluid strongly validates the basic theory of transport in unconventional superconductors. Moreover, the observed universal behavior is in quantitative agreement with calculations for a gap function of d-wave symmetry. {copyright} {ital 1997} {ital The American Physical Society}

Influence of a magnetic field on the antiferromagnetic order in UPt3.

A neutron-diffraction experiment was performed to investigate the effect of a magnetic field on the antiferromagnetic order in the heavy-fermion superconductor UPt{sub 3}. Our results show that a field in the basal plane of up to 3.2 T, higher than {ital H}{sub {ital c}2}(0), has no effect: it can neither select a domain nor rotate the moment. This has a direct impact on current theories for the superconducting phase diagram based on a coupling to the magnetic order. {copyright} {ital 1996 The American Physical Society.}

On the gap structure of UPt3: phases A and B

We have used thermal conduction and transverse sound attenuation to probe the anisotropy of the gap structure in two superconducting phases of UPt

Heat conduction in the heavy fermion superconductor UPd2Al3

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Studies of the gap structure in the heavy fermion superconductor UPt3

. For the low-temperature phase B, transverse sound has in the past provided strong evidence for a line node in the basal plane. Now, from the anisotropy of the thermal conductivity we further establish the presence of a node along the c-axis and provide information on its k-dependence. For the largely unexplored high-temperature phase A, our study of the attenuation for two directions of the polarization yields directional information on the quasiparticle spectrum, and the first clear indication of a different gap structure in the two phases.

Determination of the gap structure in UPt3 by thermal conductivity.

Abstract We present preliminary measurements of the thermal conductivity of the heavy fermion superconductor UPd 2 Al 3 for the normal and superconducting states at low temperatures. As T → 0, the superconducting state is characterized by a finite linear term, about 10% of the normal state value, which suggests a residual density of low-energy quasiparticle states. This agrees qualitatively with resonant impurity scattering theories applied to exotic superconductors with nodes in the gap structure. Comparisons are made with theory and with other U-based superconductors, such as URu 2 Si 2 and UPt 3 .

Anisotropy of heat conduction in the heavy fermion superconductor UPt3.

We have used thermal conduction and transverse sound attenuation to probe the anisotropy of the gap structure in two superconducting phases of UPt3. For the low-temperatures phase B, transverse sound has in the past provided strong evidence for a line node in the basal plane. Now, from the anisotropy of the thermal conductivity we further establish the presence of a node along the c-axis and provide information on its k-dependence. For the largely unexplored hig-temperature phase A, our study of the attenuations for two directions of the polarization yields directional information on the quasiparticle spectrum, and the first clear indication of a different gap structure in the two phases.