Quasi-One-Dimensional Spin Excitations in the Iron Pnictide NaFe0.53⁢Cu0.47⁢As

Abstract

Spectroscopic measurements in model 1D correlated systems offer insights for understanding their two-dimensional counterparts, which include the cuprate and iron pnictide/chalcogenide superconductors. A major challenge is the identification of such correlated systems with dominantly 1D physics. In this Letter, inelastic neutron scattering measurements on NaFe0.53⁢Cu0.47⁢As single crystal directly reveal quasi-1D spin excitations, resulting from atomic order that leads to magnetic Fe and nonmagnetic Cu chains. The dominant exchange interaction is antiferromagnetic along the chain [𝑆⁢𝐽∥≈90.1⁢(3)  meV], whereas the inter-chain couplings are much weaker [𝑆⁢𝐽⊥≈−2.4⁢(1)  meV and 𝑆⁢𝐽c≈0.15⁢(5)  meV]. The quasi-1D spin excitations in NaFe0.53⁢Cu0.47⁢As stem from both the Néel and stripe vectors, with Néel excitations sensitive to Fe impurities on the Cu site. The spin excitations in quasi-1D NaFe0.53⁢Cu0.47⁢As and quasi-2D FeSe exhibit a striking resemblance, suggesting a common origin for their coexistent stripe and Néel excitations. Our findings demonstrate magnetic dilution in NaFeAs leads to dimension reduction of its magnetic degree of freedom, presenting a strategy for discovering low-dimensional quantum materials.