中国物理B ›› 2013, Vol. 22 ›› Issue (8): 87413-087413.doi: 10.1088/1674-1056/22/8/087413

所属专题: TOPICAL REVIEW — Iron-based high temperature superconductors

• TOPICAL REVIEW—Iron-based high temperature superconductors • 上一篇    下一篇

Electronic phase diagram of NaFe1-xCoxAs investigated by scanning tunneling microscopy

周晓东, 蔡鹏, 王亚愚   

  1. State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
  • 收稿日期:2013-05-09 出版日期:2013-06-27 发布日期:2013-06-27
  • 基金资助:
    Project supported by the National Basic Research Program of China (Grant Nos. 2009CB929400 and 2010CB923003).

Electronic phase diagram of NaFe1-xCoxAs investigated by scanning tunneling microscopy

Zhou Xiao-Dong (周晓东), Cai Peng (蔡鹏), Wang Ya-Yu (王亚愚)   

  1. State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
  • Received:2013-05-09 Online:2013-06-27 Published:2013-06-27
  • Contact: Wang Ya-Yu E-mail:yayuwang@tsinghua.edu.cn
  • Supported by:
    Project supported by the National Basic Research Program of China (Grant Nos. 2009CB929400 and 2010CB923003).

摘要: Our recent scanning tunneling microscopy (STM) studies of the NaFe1-xCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe1-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with superconductivity in the ground state, persists well into the normal state, and shows great spatial variations.The rich electronic structures across the phase diagram of NaFe1-xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.

关键词: iron-based superconductor, scanning tunneling microscopy, spin-density wave, superconductivity

Abstract: Our recent scanning tunneling microscopy (STM) studies of the NaFe1-xCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe1-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with superconductivity in the ground state, persists well into the normal state, and shows great spatial variations.The rich electronic structures across the phase diagram of NaFe1-xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.

Key words: iron-based superconductor, scanning tunneling microscopy, spin-density wave, superconductivity

中图分类号:  (Pnictides and chalcogenides)

  • 74.70.Xa
74.25.Dw (Superconductivity phase diagrams) 74.25.Jb (Electronic structure (photoemission, etc.)) 74.55.+v (Tunneling phenomena: single particle tunneling and STM)