RESUMO
Heavy fermion compounds represent one of the most strongly correlated forms of electronic matter and give rise to low temperature states that range from small moment ordering to exotic superconductivity, both of which are often in close proximity to quantum critical points. These strong electronic correlations are associated with the transfer of entropy from the local moment degrees of freedom to the conduction electrons, and, as such, are intimately related to the low temperature degeneracy of the (originally) moment bearing ion. Here we report the discovery of six closely related Yb-based heavy fermion compounds, YbT(2)Zn(20), that are members of the larger family of dilute rare earth bearing compounds: RT(2)Zn(20) (T = Fe, Co, Ru, Rh, Os, Ir). This discovery doubles the total number of Yb-based heavy fermion materials. Given these compounds' dilute nature, systematic changes in T only weakly perturb the Yb site and allow for insight into the effects of degeneracy on the thermodynamic and transport properties of these model correlated electron systems.
Assuntos
Metais Pesados/química , Itérbio/química , Cobalto/química , Cristalização , Impedância Elétrica , Irídio/química , Ferro/química , Osmio/química , Rênio/química , Rutênio/química , Relação Estrutura-Atividade , Termodinâmica , Difração de Raios X , Óxido de Zinco/químicaRESUMO
We propose and implement a direct experimental test for subdominant superconducting phases with broken time-reversal symmetry in d-wave superconductors. The critical current of 45 degrees -asymmetric grain boundary junctions is shown to be extremely sensitive to the predicted onset of a complex order parameter at (110) surfaces and near magnetic impurities. Measurements in pure Ni-doped YBa2Cu3O7-x junctions indicate that the symmetry at the surface is consistent with pure d-wave at all temperatures, putting limits on the magnitude and chiral domain structure of any subdominant symmetry component.
