Giant Domain Walls and Intrinsic Heterogeneity in 214 Cuprate Superconductors

Abstract

The intricate interplay of structural, charge and spin orders in layered cuprates leads to emergent phenomena, most notably high-temperature superconductivity. However, there is growing awareness that both the structure and electronic ordering that underpin them are not fully homogeneous. Here, we employ scanning three-dimensional X-ray diffraction to spatially resolve structural distortions in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_{4}$, a prototypical system that exhibits a strong competition between superconductivity and charge density wave order, across its low-temperature orthorhombic to tetragonal phase transition. We uncover two forms of intrinsic microstructural heterogeneity: at 300 K, we reveal remarkably wide tetragonal-like domain wall regions within the nominally orthorhombic crystal structure, and, upon cooling to 100 K, a fine microstructure of orthorhombic-like stripes embedded within the tetragonal matrix emerges. This spatially resolved view directly defines the microstructural architecture of phase coexistence in this system, demonstrating how structural distortions generate intrinsic heterogeneity that shapes the balance between superconductivity and charge density wave order as constrained by the restrictive orthorhombic and tetragonal structures, offering a pathway to control correlated phenomena.

Figures (3)

• Figure 1: (a) Representation of the LTO (left) and LTT (right) structures, with $A$-site cation omitted for clarity. Oxygens are shown in teal and magenta indicating whether they are above and below the CuO$_2$ planes, respectively. In LTO, the sense of the distortion propagates along [010], with all layers aligned. In LTT, the sense of the distortion propagates along alternating diagonals, with a 90$^\circ$ rotation, from [110] to [1$\Bar{1}$0], between adjacent layers. (b) 300 K reconstruction of the sample from all reflection and filtered by $A$- and $B$-centred systematic absences, revealing twin domains. (c) Order parameter map indicating X$_{3}^{+}$ propagation direction with black as LTO and teal as LTT (d) 300 K strain reconstruction based on $\Gamma_{4}^{+}$ showing strong correlations with systematic absence map. Axes are given with respect to the LTO/LTT basis.
• Figure 2: Spatially resolved maps and associated histograms of symmetry-adapted strain modes at 300 K. Note the bimodal distribution of $\Gamma_{4}^{+}$, unique in capturing the twin domain structure. $\Gamma_{1}^{+}(1)$ corresponds to an in-plane symmetric expansion/contraction, while $\Gamma_{1}^{+}(2)$ is a uniform strain along $c$. $\Gamma_{2}^{+}$ is an in-plane shear strain. $\Gamma_{4}^{+}$ is the orthorhombic strain. $\Gamma_{5}^{+}(a)$ and $\Gamma_{5}^{+}(b)$ describe shear strains between the $ab$ plane and $c$ axis.
• Figure 3: (a) Spatially resolved maps of $\Gamma_{4}^{+}$ at 300 K, 140 K, 120 K and 100 K, illustrating the temperature evolution of the structural domains. (b) Histograms of $\Gamma_{4}^{+}$ at corresponding temperatures, showing the transition from bimodal at 300 K to a more homogenous but still asymmetric distribution at 100 K. (c) Maps of the absolute strain magnitude $|\Gamma_{4}^{+}|$ with (d) showing enhanced maps and line profiles, revealing broad LTT-like features within the LTO phase at 300 K and subtle LTO-like filaments within the LTT phase at 100 K. The spatial resolution of our reconstructions is at least 70 nm, see Methods.