Abstract
In copper-oxide and iron-based high-temperature (high- superconductors, many physical properties exhibit in-plane anisotropy, which is believed to be caused by a rotational symmetry-breaking nematic order, whose origin and its relationship to superconductivity remain elusive. In many iron pnictides, a tetragonal-to-orthorhombic structural transition temperature coincides with the magnetic transition temperature , making the orbital and spin degrees of freedom highly entangled. NaFeAs is a system where K is well separated from K, which helps simplify the experimental situation. Here we report nuclear magnetic resonance (NMR) measurements on that revealed orbital and spin nematicity occurring at a temperature far above in the tetragonal phase. We show that the NMR spectra splitting and its evolution can be explained by an incommensurate orbital order that sets in below and becomes commensurate below , which brings about the observed spin nematicity.
- Received 8 June 2015
- Revised 14 January 2016
DOI:https://doi.org/10.1103/PhysRevB.93.060502
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