2010/11/30 by M. Yi, Ming Yi, Dong-Hui Lu +23 · 9 citations
Materials Science · Physics and Astronomy · #Crystal Structures and Properties #Iron-based superconductors research #Rare-earth and actinide compounds #cond-mat.supr-con
paper · pdf · doi:10.1073/pnas.1015572108
published as PNAS 108, 6878 (2011) · final version published in PNAS, including supplementary information
openalex publication_date 2011/04/11 · arxiv created 2011/04/12 · arxiv updated 2012/05/15 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
Nematicity, defined as broken rotational symmetry, has recently been observed in competing phases proximate to the superconducting phase in the cuprate high-temperature superconductors. Similarly, the new iron-based high-temperature superconductors exhibit a tetragonal-to-orthorhombic structural transition (i.e., a broken C 4 symmetry) that either precedes or is coincident with a collinear spin density wave (SDW) transition in undoped parent compounds, and superconductivity arises when both transitions are suppressed via doping. Evidence for strong in-plane anisotropy in the SDW state in this family of compounds has been reported by neutron scattering, scanning tunneling microscopy, and transport measurements. Here, we present an angle-resolved photoemission spectroscopy study of detwinned single crystals of a representative family of electron-doped iron-arsenide superconductors, Ba(Fe 1- x Co x ) 2 As 2 in the underdoped region. The crystals were detwinned via application of in-plane uniaxial stress, enabling measurements of single domain electronic structure in the orthorhombic state. At low temperatures, our results clearly demonstrate an in-plane electronic anisotropy characterized by a large energy splitting of two orthogonal bands with dominant d xz and d yz character, which is consistent with anisotropy observed by other probes. For compositions x > 0, for which the structural transition ( T S ) precedes the magnetic transition ( T SDW ), an anisotropic splitting is observed to develop above T SDW , indicating that it is specifically associated with T S . For unstressed crystals, the band splitting is observed close to T S , whereas for stressed crystals, the splitting is observed to considerably higher temperatures, revealing the presence of a surprisingly large in-plane nematic susceptibility in the electronic structure.