Orbital selective spin waves in detwinned NaFeAs

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 T_s≈60 K, forming an electronic nematic phase with two 90^∘ rotated (twinned) domains, and orders antiferromagnetically below T_N≈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 E_crossover≈100 meV are dominated by d_{y z}-d_{y z} intraorbital scattering processes, which have the twofold (C₂) rotational symmetry of the underlying lattice. On the other hand, the spin wave excitations above E_crossover, which have approximately fourfold (C₄) rotational symmetry, arise from the d_{x y}-d_{x y} 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^* (>T_s ), while spin excitations at energies above E_crossover 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 T_s, thus supporting the notion of orbital selective spin waves in the nematic phase of iron-based superconductors.