d-spacing distributions as a probe of nematoelastic response in iron-based superconductors

2026/08/02 by Wenting Zhang, Ruixian Liu, Tingjun Zhang +14
Physics and Astronomy · #cond-mat.supr-con #cond-mat.str-el

paper · pdf

9 pages, 4 figures

arxiv created 2026/08/02 · arxiv updated 2026/08/04

Abstract

Electronic nematicity in iron-based superconductors (FeSCs) couples bilinearly to orthorhombic strain, allowing nematic correlations to appear in the lattice response. Here we use neutron Larmor diffraction to measure the temperature-dependent distribution of relative d spacings in electron-doped Ba(Fe_1-xCo_x)₂As₂, hole-doped Ba_0.83K_0.17Fe₂As₂, FeSe, and Fe_1.07Te. In Ba(Fe_1-xCo_x)₂As₂ crystals without intentionally applied uniaxial stress, the in-plane distribution width, ε_{\rm FWHM}, increases on cooling in the tetragonal phase and can be described phenomenologically by a Curie--Weiss-like form. The fitted scale T^* decreases with Co doping and evolves similarly to the nematic phase diagram inferred from elastoresistance, although the two experiments probe different response functions. Related broadening in Ba_0.83K_0.17Fe₂As₂ and FeSe supports extending this interpretation beyond electron-doped BaFe₂As₂. By contrast, Fe_1.07Te shows no extended Curie--Weiss-like regime without applied stress, whereas uniaxial pressure produces a strongly anisotropic broadening that can contain contributions from both the field-biased lattice response and inhomogeneous loading. A mean-field model with bilinear nematoelastic coupling and spatially varying symmetry-breaking stress explains the Curie--Weiss-like broadening in terms of the renormalized orthorhombic compliance. Neutron Larmor diffraction therefore provides a bulk-sensitive probe of nematic-related lattice broadening that complements electronic and elastic measurements.