Zeeman magnetic field responses of d-wave superconductors observed by tunneling spectroscopy

Abstract Spin polarized tunneling spectroscopy was applied to optimally doped Yba 2 Cu 3 O 7− δ (YBCO) in order to detect the quasiparticle spin properties of d -wave superconducting phase. YBCO/La 0.67 Sr 0.33 MnO 3 epitaxial junctions were fabricated by PLD and photolithographic process and a magnetic field was applied to the direction parallel to the ab -plane. Both on (110) and (100) oriented junctions, the expected Zeeman splitting of conductance spectrum was not detected up to 14 T even though the conductance peaks have enough sharpness to detect the splitting. This feature is quite inconsistent with weak coupling BCS model, which takes into account of d -wave symmetry. The results are explained in terms of that the high- T c oxides are not ordinary Fermi-liquid superconductors.