Orbital selective spin waves in detwinned NaFeAs

摘要

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_(yz)-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_(crossover), which have approximately fourfold (C_4) rotational symmetry, arise from the d_(xy)-d)(xy) 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 C_4 to C_2 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 Ts, thus supporting the notion of orbital selective spin waves in the nematic phase of iron-based superconductors.