Superconductivity And Magnetism In D- And F- Electron Compounds

The interaction of electrons with different degrees of freedom in correlated matters leads to many important physical discoveries,such as high temperature superconductivity,colossal magnetoresistance and multiferroics.At present,research mainly focuses on transition metal compounds containing 3d electrons.For instance,the main contribution to superconductivity in cuprates and iron-based superconductors comes from the 3d electrons in copper and iron,respectively.For materials with higher orbital electrons,such as 4d,4f and 5d,the degree of electronic localization decreases,which shows the dual properties of itinerancy/localization.At the same time,the spin-orbit coupling also increases.These two effects result in more exotic physical properties.This thesis will mainly focus on two parts.Part one is superconductivity and multiple quantum phase transitions in CeRhIn5,which is a heavy fermion material possessing 4f electrons.Part two is superconductivity and vortices in the d-electron materials Lu3Os4 Ge13 and Y3Ru4Ge13.The antiferromagnetic compound CeRhIn5 is an ideal system for studying the interaction between quantum phase transitions and heavy fermion superconductivity.Through dHvA and Hall effect measurements,a Fermi surface reconstruction is observed at around B*? 30T and an SDW type antiferromagnetic quantum critical point is found at 50T,which is completely different from the pressure induced antiferromagnetic quantum critical point.This thesis focuses on the evolution of the antiferromagnetic phase transition and Fermi surface of CeRhIns under pressure and in magnetic fields,where the pressure-field phase diagram of the compound has been preliminarily determined.When the applied magnetic field is along the a-axis,the antiferromagnetic transition temperature of CeRhIn5 decreases with increasing pressure.When the magnetic field is along the c-axis,a richer pressure field phase diagram is obtained.When the magnetic field is parallel to the c-axis,the resistivity shows a sudden jump in low magnetic fields BM,and BM increases with pressure,which is probably due to the metamagnetic transition.The field induced Fermi surface reconstruction is investigated by Hall resistance measurements and the value of B*barely changes.Our preliminary results still need further verification and experiments.The second part of the thesis focuses on the 4d/5d electronic systems Lu3Os4Ge13 and Y3 Ru4 Ge13.We systematically studied the superconducting properties of these two compounds by resistivity,ac susceptibility and penetration depth measurements.The analysis of the penetration depth and the derived superfluid density indicates the presence of nodeless superconductivity and suggests that there are multiple superconducting gaps in both materials.Furthermore,ac susceptibility measurements of both compounds display the peak effect in the low-temperature region.This anomalous increase of the critical current with field indicates a change of the arrangement of flux lines in the mixed state.