Origin of metal–insulator transition in the weak-ferromagnetic superconductor system RuSr2RCu2O8 (R = rare earths)

摘要: Abstract For the oxygen-annealed weak-ferromagnetic superconductor system RuSr 2 RCu O 8 (R = rare earths), superconducting transition temperature T sc decreases steadily from maximum 56 K for smaller rare earth Gd 3+ (ionic radius r  = 0.105 nm), to 54 K (Eu 0.5 ) , 36 K Eu 8 K (Sm and metallic but not larger Sm (  = 0.108 nm), with a metal–insulator even ions Nd  = 0.112 nm) Pr  = 0.113 nm). Powder X-ray diffraction Rietveld refinement study indicates that insulating phase is stabilized in undistorted tetragonal (space group P4 / mmm lattice parameter  ∼ 0.390–392 nm, which gives reasonable Ru 5+ –O bond length of d  ∼ 0.197 nm. On other hand, can be only distorted mbm ), /√2 ∼ 0.383–0.385 nm still provide Ru–O through RuO 6 octahedron rotation. The as well variation closely related oxygen deficiency content δ control mobile hole concentration structural this hole-doped system.