Spin dynamics in NaFeAs and NaFe0.53Cu0.47As probed by resonant inelastic x-ray scattering

Abstract

The parent compounds of iron-based superconductors are magnetically ordered bad metals, with superconductivity appearing near a putative magnetic quantum critical point. The presence of both Hubbard repulsion and Hund's coupling leads to rich physics in these multiorbital systems, and motivated descriptions of magnetism in terms of itinerant electrons or localized spins. The NaFe 1−x Cu x As series consists of magnetically ordered bad metal (x = 0), superconducting (x ≈ 0.02) and magnetically ordered semiconducing/insulating (x ≈ 0.5) phases, providing a platform to investigate the connection between superconductivity, magnetism and electronic correlations. Here we use x-ray absorption spectroscopy and resonant inelastic x-ray scattering to study the valence state of Fe and spin dynamics in two NaFe 1−x Cu x As compounds (x = 0 and 0.47). We find that magnetism in both compounds arises from Fe 2+ atoms, and exhibits underdamped dispersive spin waves in their respective ordered states. The dispersion of spin excitations in NaFe 0.53 Cu 0.47 As is consistent with being quasi-one-dimensional. Compared to NaFeAs, the band top of spin waves in NaFe 0.53 Cu 0.47 As is slightly softened with significantly more spectral weight of the spin excitations. Our results indicate the spin dynamics in NaFe 0.53 Cu 0.47 As arise from localized magnetic moments and suggest the iron-based superconductors are proximate to a correlated insulating state with localized iron moments.

RKKY coupled local moment magnetism in NaFe$_{1-x}$Cu$_{x}$As

“…In contrast, for low concentrations x as we report here, the Cu dopants are found to be electron doping, suggesting that they are magnetic with valence 2+ [12,20]. The magnetic Fe ions are in the same valence state as the dopants [19]. In this case, it is not yet clear whether antiferromagnetism follows a local moment picture or is itinerant, associated with Fermi surface nesting [21][22][23][24][25][26][27][28].…”

“…In the heavily doped regime (x ≈ 0.5) it is a Mott insulator while for low copper doping concentrations (x ≤ 0.05) it is metallic, exhibiting superconductivity in close proximity to an AFM ordered state [12,13]. At high doping long-range AFM order arises from localized moments on the Fe sites [14][15][16][17][18] and the Cu dopants are nonmagnetic in a valence state Cu 1+ with completely filled 3d orbitals [14,19]. We have previously studied this regime [17,18] using 23 Na NMR showing that long range order is only achieved for x very close to 0.5; otherwise, the magnetic state is an spin glass as exemplified in the case x = 0.39 [Fig.…”

Magnetic excitations in iron-based superconductors as revealed by resonant inelastic X-ray scattering

“…Fe K-β X射线发射谱是一种能够测量Fe离子自 旋态和局域磁矩的实验技术. Gretarsson等人 [32,33] [29] 针 对111体 系, Song等 人 [34] 在2021年 报 道 了Na- 2019年, Garcia等 人 [35] 测 量 了Ba(Fe 1−x Mn x ) 2 As 2 (x = 0, 0.007, 0.009, 0.08…”

“…铁基超导体的RIXS谱的谱重通常被E 0.5 eV 表 表 表 1 铁基超导材料中元激发的RIXS研究列表(部分). ∆E表示RIXS谱仪分辨率, SE (Spin Excitations)表示磁激发 [22] ADRESS 70 N Y Ba 1−x K x Fe 2 As 2 (x = 0, 0.4) [19] ADRESS ADRESS 90 Y Y NaFe 1−x Co x As (x = 0, 0.03, 0.08) [26] ADRESS 110 Y Y NaFe 1−x Cu x As (x = 0, 0.47) [34] ADRESS 86 Y Y PrFeAsO 0.7 [44] BL07SU@Spring-8 230 N N SmFeAsO [27] ADRESS 110 Y N FeSe [36] ID32@ESRF 55 Y Y Detwinned FeSe [21] ADRESS 80 Y N Uniaxial-strained FeSe 1−x S x ADRESS 80 Y N Monolayer FeSe/SrTiO 3 [40] I21@Diamond 40 Y N/A (Li,Fe)OHFeSe [42] ADRESS 80 N bulk (Li 0.8 Fe 0.2 )ODFeSe [43] 的荧光信号主导. 精确描述荧光谱对提取磁散射信 号十分重要.…”