arXiv subjects

Ella M. Schmidt

Publications and source records attributed to Ella M. Schmidt.

7 recordsLinked to original sources

arXiv2026

Symmetry-Selective Stabilization of Charge-Density Wave in ScV$_6$Sn$_6$

Charge-density-wave (CDW) order in kagome metals is highly sensitive to external tuning parameters such as chemical substitution and hydrostatic pressure, which generally suppress long-range order. Here, using high-resolution X-ray diffraction under controlled uniaxial strain, we show that anisotropic lattice deformation instead stabilizes and enhances the CDW state in ScV$_6$Sn$_6$. Compression along the [H00] and [HH0] directions lowers the crystal symmetry from hexagonal to orthorhombic, lifts the degeneracy between symmetry-equivalent in-plane CDW domains, and promotes long-range order while preserving the underlying trimer instability. Phonon calculations indicate only a moderate stabilization of the imaginary flat phonon mode, demonstrating that the increase in T$_\mathrm{CDW}$ is primarily driven by the in-plane ordering of the Sn$^\mathrm{T}$--Sc--Sn$^\mathrm{T}$ \textit{rattling} chains within the frustrated kagome lattice. A phenomenological model incorporating strain-dependent Ising couplings within a three-state Potts framework successfully reproduces the evolution of T$_\mathrm{CDW}$ under compression and captures the continuous nature of the transition. Our results establish uniaxial strain as a powerful symmetry-selective tuning parameter for order-disorder transformations in frustrated lattices.

cond-mat.str-el↗

arXiv2024

Disentangling competing interactions in disordered materials using interaction space modelling

Understanding and manipulating the relationship between intentionally introduced disorder and material properties necessitates efficient characterization techniques. For example, single crystal diffuse scattering experiments provide insights into the driving forces behind local order phenomena. In this work, we present a time- and resource-efficient approach based on mean field theory, that quantifies local interaction energies but unlike other techniques does not require computationally expensive supercell models. The method is employed to quantify competing interactions in functionally disordered materials such as disordered rock salt cathode materials and Prussian blue analogs that share an underlying face-centred lattice.

cond-mat.mtrl-sci↗

arXiv2022

Direct interpretation of the X-ray and neutron 3D-$Δ$PDFs of yittria stabilized zirconia

Three dimensional difference pair distribution functions from X-ray and neutron diffraction experiments are reported for yttria stabilized zirconia (Zr$_{0.82}$Y$_{0.18}$O$_{1.91}$). We use a quantitative analysis of the signatures in the 3D-$Δ$PDFs to establish that oxygen ions neighbouring a vacancy shift by 0.515(5)~Å along $\langle 1,0,0 \rangle$ towards the vacancy while metal ions neighbouring a vacancy shift by 0.269(2)~Å along $\langle 1,1,1 \rangle$ away from the vacancy. The neutron 3D-$Δ$PDF shows a tendency for vacancies to cluster along $\langle \frac{1}{2},\frac{1}{2},\frac{1}{2}\rangle$, which results in 6-fold coordinated metal ions.

cond-mat.mtrl-sci↗

arXiv2022

Truchet-tile structure of a topologically aperiodic metal-organic framework

Periodic tilings can store information if individual tiles are decorated to lower their symmetry. Truchet tilings - the broad family of space-filling arrangements of such tiles - offer an efficient mechanism of visual data storage related to that used in barcodes and QR codes. Here, we show that the crystalline metal-organic framework [OZn$_4$][1,3-benzenedicarboxylate]$_3$ (TRUMOF-1) is an atomic-scale realisation of a complex three-dimensional Truchet tiling. Its crystal structure consists of a periodically-arranged assembly of identical zinc-containing clusters connected uniformly in a well-defined but disordered fashion to give a topologically aperiodic microporous network. We suggest that this unusual structure emerges as a consequence of geometric frustration in the chemical building units from which it is assembled.

cond-mat.mtrl-sci↗

arXiv2021

Efficient fitting of single-crystal diffuse scattering in interaction space: a mean-field approach

The diffraction patterns of crystalline materials with strongly-correlated disorder are characterised by the presence of structured diffuse scattering. Conventional analysis approaches generally seek to interpret this scattering either atomistically or in terms of pairwise (Warren--Cowley) correlation parameters. Here we demonstrate how a mean-field methodology allows efficient fitting of diffuse scattering directly in terms of a microscopic interaction model. In this way the approach gives as its output the underlying physics responsible for correlated disorder. Moreover, the use of a very small number of parameters during fitting renders the approach surprisingly robust to data incompleteness, a particular advantage when seeking to interpret single-crystal diffuse scattering measured in complex sample environments. We use as the basis of our proof-of-concept study a toy model based on strongly-correlated disorder in diammine mercury(II) halides.

cond-mat.dis-nn↗

arXiv2016

Spectral properties of unimodular lattice triangulations

Random unimodular lattice triangulations have been recently used as an embedded random graph model, which exhibit a crossover behaviour between an ordered, large-world and a disordered, small-world behaviour. Using the ergodic Pachner flips that transform such triangulations into another and an energy functional that corresponds to the degree distribution variance, Markov chain Monte-Carlo simulations can be applied to study these graphs. Here, we consider the spectra of the adja cency and the Laplacian matrix as well as the algebraic connectivity and the spectral radius. Power law dependencies on the system size can clearly be identified and compared to analytical solutions for periodic ground states. For random triangulations we find a qualitative agreement of the spectral properties with well-known random graph models. In the microcanonical ensemble analytical approximations agree with numerical simulations. In the canonical ensemble a crossover behaviour can be found for the algebraic connectivity and the spectral radius, thus combining large-world and small-world behavior in one model. The considered spectral properties can be applied to transport problems on triangulation graphs and the crossover behaviour allows a tuning of important transport quantities.

cond-mat.dis-nn↗

arXiv2015

Unimodular lattice triangulations as small-world and scale-free random graphs

Real-world networks, e.g. the social relations or world-wide-web graphs, exhibit both small-world and scale-free behaviour. We interpret lattice triangulations as planar graphs by identifying triangulation vertices with graph nodes and one-dimensional simplices with edges. Since these triangulations are ergodic with respect to a certain Pachner flip, applying different Monte-Carlo simulations enables us to calculate average properties of random triangulations, as well as canonical ensemble averages using an energy functional that is approximately the variance of the degree distribution. All considered triangulations have clustering coefficients comparable with real world graphs, for the canonical ensemble there are inverse temperatures with small shortest path length independent of system size. Tuning the inverse temperature to a quasi-critical value leads to an indication of scale-free behaviour for degrees $k \geq 5$. Using triangulations as a random graph model can improve the understanding of real-world networks, especially if the actual distance of the embedded nodes becomes important.

cond-mat.dis-nn↗