Abstract
The existence of orbital-dependent electronic correlations has been recognized as an essential ingredient to describe the physics of iron-based superconductors. NaFeAs, a parent compound of iron-based superconductors, exhibits a tetragonal-to-orthorhombic lattice distortion below Ts≈60 K, forming an electronic nematic phase with two 90∘ rotated (twinned) domains, and orders antiferromagnetically below TN≈42 K. We use inelastic neutron scattering to study spin waves in uniaxial pressure-detwinned NaFeAs. By comparing the data with combined density functional theory and dynamical mean-field theory calculations, we conclude that spin waves up to an energy scale of Ecrossover≈100 meV are dominated by dyz−dyz intraorbital scattering processes, which have the twofold (C2) rotational symmetry of the underlying lattice. On the other hand, the spin wave excitations above Ecrossover, which have approximately fourfold (C4) rotational symmetry, arise from the dxy−dxy intraorbital scattering that controls the overall magnetic bandwidth in this material. In addition, we find that the low-energy (E≈6 meV) spin excitations change from approximate C4 to C2 rotational symmetry below a temperature T∗ (>Ts), while spin excitations at energies above Ecrossover have approximate C4 rotational symmetry and are weakly temperature dependent. These results are consistent with angle-resolved photoemission spectroscopy measurements, where the presence of a uniaxial strain necessary to detwin NaFeAs also raises the onset temperature T∗ of observable orbital-dependent band splitting to above Ts, thus supporting the notion of orbital selective spin waves in the nematic phase of iron-based superconductors.
