Superconductivity In UPd2Al3 Research Articles

Magnetic-exciton-mediated superconductivity in UPd2Al3

Abstract There is compelling evidence from inelastic neutron scattering and tunnelling experiments that the heavy fermion superconductor UPd2Al3 can be understood as a dual system consisting of magnetic excitons, arising from crystal-field-split U4+ levels, coupled to delocalised f electrons [N. Sato, et al., Nature 410 (2001) 340 [1] ]. We have computed the superconducting transition temperature and the mass renormalisation arising from a dual model with maximal spin anisotropy using a strong-coupling approach [P. McHale, et al., Phys. Rev. B 70 (2004) 014513 [2] ]. We find that superconducting states with a line node in the ab-plane are favoured in agreement with NMR relaxation-rate, specific-heat and thermal-conductivity measurements. The signature of line nodes on the low temperature field-angle resolved magnetothermal conductivity in the vortex phase of UPd2Al3, as investigated in T. Watanabe, et al., cond-mat/0405211 [3] , is studied within the Doppler shift approximation for the quasiparticle energies.

Gap symmetry of superconductivity in UPd2Al3

The angle dependent thermal conductivity of the heavy-fermion superconductor UPd$_2$Al$_3$ in the vortex state was recently measured by Watanabe et al. Here we analyze this data from two perspectives: universal heat conduction and the angle-dependence. We conclude that the superconducting gap function $\Delta({\bf k})$ in UPd$_2$Al$_3$ has horizontal nodes and is given by $\Delta({\bf k}) =\Delta\cos(2\chi)$, with $\chi = ck_{z}$.

Superconductivity Through Intra-Atomic Excitations

It is demonstrated that the occurring of superconductivity in UPd2Al3 can be understood within the dual model for 5f electrons. Due to strong intra-atomic or Hund’s rule correlations two of the 5f electrons remain localized while the remaining 5f part is delocalized and part of the conduction electrons. Cooper-pair formation of the latter takes place due to the exchange of magnetic excitations within the localized 5f subsystem. By solving Eliashberg’s equations, it is shown that a consistent description can be obtained of the superconducting transition temperature and of the strong mass anisotropies of the semi-heavy quasiparticles.