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 $T_s\approx 60$ K, forming an electronic nematic phase with two ${90}^{\circ }$ rotated (twinned) domains, and orders antiferromagnetically below $T_N\approx 42$ 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 $E_{\text{crossover}}\approx 100$ meV are dominated by $d_{yz}\text{−}{d}_{yz}$ intraorbital scattering processes, which have the twofold ($C_2$) rotational symmetry of the underlying lattice. On the other hand, the spin wave excitations above $E_{\text{crossover}}$, which have approximately fourfold ($C_4$) rotational symmetry, arise from the $d_{xy}\text{−}{d}_{xy}$ intraorbital scattering that controls the overall magnetic bandwidth in this material. In addition, we find that the low-energy ($E\approx 6$ meV) spin excitations change from approximate $C_4$ to $C_2$ rotational symmetry below a temperature $T^{*}$ ($>T_s$), while spin excitations at energies above $E_{\text{crossover}}$ have approximate $C_4$ 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.

• Received 27 December 2019
• Revised 28 July 2020
• Accepted 31 July 2020

DOI:https://doi.org/10.1103/PhysRevB.102.054430