Damping mechanism for the strongly renormalized cc-axis charge transport in high-TcT_c cuprate superconductors

We analyze the $c$-axis infrared reflectivity of La$_{1.85}$Sr$_{0.15}$CuO$_4$ single crystals. The plasma edge near 6 meV, observed below $T_c$, is due to Cooper-pair tunneling. This low value of the plasma edge is consistent with the $c$-axis plasma frequency ($\nu_p$) obtained from LDA calculations ($>0.1$ eV) if we take into account that the single-particle charge transport along the $c$ axis is strongly incoherent both above and below $T_c$. We find no evidence for a reduction of the $c$-axis scattering rate ($\gamma$) below $T_c$. Our investigation suggests $h\gamma>h\nu_{p}\gg 3.5k_BT_c$, which is exactly opposite to the clean limit. VSGD.94.6.1Comment: 4 pages, figures on request. Revtex, version 2, Materials Science Center Internal Report Number VSGD.94.6.

Direct evidence for critical exchange coupling via Allayers in the heavy fermion compound CePd2Al3

The long-range planar-type antiferromagnetic ordering in the heavy-fermion compound CePd2Al3 is shown to critically depend on the exact occupation and distribution of aluminum atoms over their available lattice sites. A poly-crystalline sample (TN=2.7 K) is systematically compared with a nonordering single crystal, by means of susceptibility, specific heat, and site-specific Al-NQR/NMR experiments. Implications for other Al-containing heavy-fermion systems are discussed