2011年4月，我室低维物理与化学研究部陈仙辉教授研究组与复旦大学等单位合作在NATURE MATERIALS上发表题为Nodeless superconducting gap in A(x)Fe(2)Se(2) (A = K, Cs) revealed by angle-resolved photoemission spectroscopy的论文。

Source: NATURE MATERIALS Volume: 10 Issue: 4 Pages: 273-277 Published: APR 2011
Zhang Y (Zhang, Y.)1,2, Yang LX (Yang, L. X.)1,2, Xu M (Xu, M.)1,2, Ye ZR (Ye, Z. R.)1,2, Chen F (Chen, F.)1,2, He C (He, C.)1,2, Xu HC (Xu, H. C.)1,2, Jiang J (Jiang, J.)1,2, Xie BP (Xie, B. P.)1,2, Ying JJ (Ying, J. J.)3,4, Wang XF (Wang, X. F.)3,4, Chen XH (Chen, X. H.)3,4, Hu JP (Hu, J. P.)5, Matsunami M (Matsunami, M.)6,7, Kimura S (Kimura, S.)6,7, Feng DL (Feng, D. L.)1,2
Addresses:
1. Fudan Univ, State Key Lab Surface Phys, Adv Mat Lab, Shanghai 200433, Peoples R China
2. Fudan Univ, Dept Phys, Shanghai 200433, Peoples R China
3. Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Hefei 230026, Anhui Peoples R China
4. Univ Sci & Technol China, Dept Phys, Hefei 230026, Anhui Peoples R China
5. Purdue Univ, Dept Phys, W Lafayette, IN 47907 USA
6. UVSOR Facil, Inst Mol Sci, Okazaki, Aichi 4448585 Japan
7. Grad Univ Adv Studies, Okazaki, Aichi 4448585 Japan
E-mail Addresses: dlfeng@fudan.edu.cn

Reprint Address: Feng, DL (reprint author), Fudan Univ, State Key Lab Surface Phys, Adv Mat Lab, Shanghai 200433, Peoples R China

Abstract:
Pairing symmetry is a fundamental property that characterizes a superconductor. For the iron-based high-temperature superconductors, an s(+/-)-wave pairing symmetry has received increasing experimental and theoretical support. More specifically, the superconducting order parameter is an isotropic s-wave type around a particular Fermi surface, but it has opposite signs between the hole Fermi surfaces at the zone centre and the electron Fermi surfaces at the zone corners. Here we report the low-energy electronic structure of the newly discovered superconductors, A(x)Fe(2)Se(2) (A = K, Cs) with a superconducting transition temperature (T-c) of about 30 K. We found A(x)Fe(2)Se(2) (A = K, Cs) is the most heavily electron-doped among all iron-based superconductors. Large electron Fermi surfaces are observed around the zone corners, with an almost isotropic superconducting gap of similar to 10.3 meV, whereas there is no hole Fermi surface near the zone centre, which demonstrates that interband scattering or Fermi surface nesting is not a necessary ingredient for the unconventional superconductivity in iron-based superconductors. Thus, the sign change in the s(+/-) pairing symmetry driven by the interband scattering as suggested in many weak coupling theories becomes conceptually irrelevant in describing the superconducting state here. A more conventional s-wave pairing is probably a better description.