Rare earth ion effects on the pseudo-gap in electron-doped superconductors and possible nodeless d-wave gap

• Published in: The Journal of physics and chemistry of solids Vol. 69; no. 12; pp. 2939 - 2943
• Main Authors: Park, S.R., Leem, C.S., Roh, Y.S., Choi, K.J., Kim, J.H., Kim, B.J., Koh, H., Eisaki, H., Lu, D.H., Shen, Z.-X., Armitage, N.P., Kim, C.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2008; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic properties; Physics; Properties of type I and type II superconductors; Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.); Superconductivity; 79.60.−i; 74.25.Jb; 74.72.−h; Quasiparticles; d-wave superconductivity; Electronic structure; Fermi level; Hole density; Doping; High-Tc superconductors; Angle resolved photoemission spectroscopy; Chemical composition; Excited states; Cerium Copper Samarium Oxides Mixed
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2008.06.116

We report angle resolved photoemission (ARPES) studies on electron-doped cuprate superconductor Sm 2 - x Ce x CuO 4 ( x = 0.14 and 0.18). A wide energy range scan shows clear “waterfall” effect at an energy scale close to 500 meV which is consistent with the value found in Nd 2 - x Ce x CuO 4 (NCCO) but larger than that from hole-doped superconductors. High resolution results from both dopings show pseudo-gap effects that were observed in NCCO. However, the effects are found to be stronger than that observed in optimally doped NCCO. The overall electronic structure is well understood within a simple model in which a 2 × 2 static order is assumed. Both ARPES and optical measurements give the coupling strengths to the Q =( π / 2 , π / 2 ) (due to the 2 × 2 order) to be about 0.1 eV, compatible with each other. The effect is strong enough to push the band near the nodal region below the Fermi energy, resulting in possible nodeless d-wave superconductivity where zero energy quasi-particle excitation is inhibited.