Arkadiy Simonov

Last Name

Simonov

First Name

Arkadiy

ORCID

0000-0003-1342-2168

Organisational unit

09778 - Simonov, Arkadiy / Simonov, Arkadiy

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Publications 1 - 10 of 35

The Mystery of the AuIn 1:1 Phase and Its Incommensurate Structural Variations
Folkers, Laura C.; Simonov, Arkadiy; Wang, Fei; et al. (2018)
Inorganic Chemistry
In this communication, the AuIn 1:1 phase ( Naturwissenschaften, 1953, 40, 437, DOI: 10.1007/BF00590353), and its ordering behavior at various temperatures is investigated. To enable the growth of a X-ray suitable specimen, a tempering routine was established by the interpretation of a differential scanning calorimetry (DSC) study. In this way, good quality single crystals were grown and measured at the Crystal beamline at Synchrotron SOLEIL. From the acquired data, three variations of this structure could be found at temperatures of 400 °C and 300 °C and room temperature, with differing degrees of incommensurate modulation. Diffuse scattering found at 400 °C was interpreted with the help of a three-dimensional difference pair distribution function (3D-ΔPDF) study.
Structure of decagonal Al-Ni-Rh
Logvinovich, Dmitry; Simonov, Arkadiy; Steurer, Walter (2014)
Acta Crystallographica Section B: Structural Science
Emerging spin-phonon coupling through cross-talk of two magnetic sublattices
Weber, Mads C.; Guennou, Mael; Evans, Donald M.; et al. (2022)
Nature Communications
Many material properties such as superconductivity, magnetoresistance or magnetoelectricity emerge from the non-linear interactions of spins and lattice/phonons. Hence, an in-depth understanding of spin–phonon coupling is at the heart of these properties. While most examples deal with one magnetic lattice only, the simultaneous presence of multiple magnetic orderings yield potentially unknown properties. We demonstrate a strong spin–phonon coupling in SmFeO3 that emerges from the interaction of both, iron and samarium spins. We probe this coupling as a remarkably large shift of phonon frequencies and the appearance of new phonons. The spin–phonon coupling is absent for the magnetic ordering of iron alone but emerges with the additional ordering of the samarium spins. Intriguingly, this ordering is not spontaneous but induced by the iron magnetism. Our findings show an emergent phenomenon from the non-linear interaction by multiple orders, which do not need to occur spontaneously. This allows for a conceptually different approach in the search for yet unknown properties.
The three-dimensional pair distribution function analysis of disordered single crystals
Weber, Thomas; Simonov, Arkadiy (2012)
Zeitschrift für Kristallographie
Phonon broadening from supercell lattice dynamics: Random and correlated disorder
Overy, Alistair R.; Simonov, Arkadiy; Chater, Philip A.; et al. (2017)
Physica Status Solidi B
We demonstrate how supercell implementations of conventional lattice dynamical calculations can be used to determine the extent and nature of disorder-induced broadening in the phonon dispersion spectrum of disordered crystalline materials. The approach taken relies on band unfolding, and is first benchmarked against virtual crystal approximation phonon calculations. The different effects of mass and interaction disorder on the phonon broadening are then presented, focussing on the example of a simple cubic binary alloy. For the mass disorder example, the effect of introducing correlated disorder is also explored by varying the fraction of homoatomic and heteroatomic neighbors. Systematic progression in the degree of phonon broadening, on the one hand, and the form of the phonon dispersion curves from primitive to face-centered cubic type, on the other hand, is observed as homoatomic neighbors are disfavored. The implications for rationalizing selection rule violations in disordered materials and for using inelastic neutron scattering measurements as a means of characterizing disorder are discussed.
Elucidating 2D Charge-Density-Wave Atomic Structure in an MX–Chain by the 3D-ΔPair Distribution Function Method
Guérin, Laurent; Yoshida, Takefumi; Zatterin, Edoardo; et al. (2022)
ChemPhysChem
Many solids, particularly low-dimensional systems, exhibit charge density waves (CDWs). In one dimension, charge density waves are well understood, but in two dimensions, their structure and their origin are difficult to reveal. Herein, the 2D charge-density-wave atomic structure and stabilization mechanism in the bromide-bridged Pd compound [Pd(cptn)(2)Br]Br-2 (cptn =1R,2R-diaminocyclopentane) is investigated by means of single-crystal X-ray diffraction employing the 3D-Delta pair distribution function (3D-Delta PDF) method. Analysis of the diffuse scattering using 3D-Delta PDF shows that a 2D-CDW is stabilized by a hydrogen-bonding network between Br+ counteranion and the amine (NH2) group of the cptn in-plane ligand, and that 3D ordering is prevented due to a weak plane to plane correlation. We extract the effective displacements of the atoms describing the atomic structure quantitatively and discuss the stabilization mechanism of the 2D-CDW. Our study provides a method to identify and measure the key interaction responsible for the dimensionality and stability of the CDW that can help further progress of rational design.
Hybrid local-order mechanism for inversion symmetry breaking
Wolpert, Emma H.; Overy, Alistair R.; Thygesen, Peter M.M.; et al. (2018)
Physical Review B
Using classical Monte Carlo simulations, we study a simple statistical mechanical model of relevance to the emergence of polarization from local displacements on the square and cubic lattices. Our model contains two key ingredients: a Kitaev-like orientation-dependent interaction between nearest neighbors and a steric term that acts between next-nearest neighbors. Taken by themselves, each of these two ingredients is incapable of driving long-range symmetry breaking, despite the presence of a broad feature in the corresponding heat-capacity functions. Instead, each component results in a “hidden” transition on cooling to a manifold of degenerate states; the two manifolds are different in the sense that they reflect distinct types of local order. Remarkably, their intersection, i.e., the ground state when both interaction terms are included in the Hamiltonian, supports a spontaneous polarization. In this way, our study demonstrates how local-order mechanisms might be combined to break global inversion symmetry in a manner conceptually similar to that operating in the “hybrid” improper ferroelectrics. We discuss the relevance of our analysis to the emergence of spontaneous polarization in well-studied ferroelectrics such as BaTiO3 and KNbO3.
Pronounced interplay between intrinsic phase-coexistence and octahedral tilt magnitude in hole-doped lanthanum cuprates
Tidey, Jeremiah P.; Liu, En-Pei; Lai, Yen-Chung; et al. (2022)
Scientific Reports
Definitive understanding of superconductivity and its interplay with structural symmetry in the hole-doped lanthanum cuprates remains elusive. The suppression of superconductivity around 1/8th doping maintains particular focus, often attributed to charge-density waves (CDWs) ordering in the low-temperature tetragonal (LTT) phase. Central to many investigations into this interplay is the thesis that La$_1$$_.$$_8$$_7$$_5$Ba$_0$$_.$$_1$$_2$$_5$CuO$_4$ and particularly La$_1$$_.$$_6$$_7$$_5$Eu$_0$$_.$$_2$Sr$_0$$_.$$_1$$_2$$_5$CuO$_4$ present model systems of purely LTT structure at low temperature. However, combining single-crystal and high-resolution powder X-ray diffraction, we find these to exhibit significant, intrinsic coexistence of LTT and low-temperature orthorhombic domains, typically associated with superconductivity, even at 10 K. Our two-phase models reveal substantially greater tilting of CuO$_6$ octahedra in the LTT phase, markedly buckling the CuO$_2$ planes. This would couple significantly to band narrowing, potentially indicating a picture of electronically driven phase segregation, reminiscent of optimally doped manganites. These results call for reassessment of many experiments seeking to elucidate structural and electronic interplay at 1/8 doping.
Giant Modulation of Refractive Index from Picoscale Atomic Displacements
Zhao, Boyang; Ren, Guodong; Mei, Hongyan; et al. (2024)
Advanced Materials
It is shown that structural disorder—in the form of anisotropic, picoscale atomic displacements—modulates the refractive index tensor and results in the giant optical anisotropy observed in BaTiS₃, a quasi-1D hexagonal chalcogenide. Single-crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS₆ chains along the c-axis, and threefold degenerate Ti displacements in the a–b plane. ⁴⁷/⁴⁹Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from a low symmetry local environment around Ti atoms. Scanning transmission electron microscopy is used to directly observe the globally disordered Ti a–b plane displacements and find them to be ordered locally over a few unit cells. First-principles calculations show that the Ti a–b plane displacements selectively reduce the refractive index along the ab-plane, while having minimal impact on the refractive index along the chain direction, thus resulting in a giant enhancement in the optical anisotropy. By showing a strong connection between structural disorder with picoscale displacements and the optical response in BaTiS₃, this study opens a pathway for designing optical materials with high refractive index and functionalities such as large optical anisotropy and nonlinearity.
Origin of correlated diffuse scattering in the hexagonal manganites
Tosic, Tara Niamh; Deen, Pascale P.; Simonov, Arkadiy; et al. (2024)
Physical Review Research
We use a combination of first-principles density-functional calculations and spin-dynamics simulations to explain the unusual diffuse inelastic neutron scattering in the hexagonal multiferroic yttrium manganite, YMnO3. Using symmetry considerations, we construct a model spin Hamiltonian with parameters derived from our density-functional calculations and show that it captures the measured behavior. We then show that the observed directionality in the structured diffuse scattering in momentum space is a hallmark of the triangular geometry, and that its persistence across a wide range of temperatures, both above and below the Néel temperature TN , is a result of the strong magnetic frustration. We predict that this diffuse scattering exists in a yet-to-be-observed modulated continuum of energies, that its associated spin excitations have distinct in-plane and out-of-plane character, and that vestiges of the magnetic frustration persist into the sub-TN state. Finally, we show that visualizing the magnetic order in terms of composite trimer magnetoelectric monopoles and toroidal moments, rather than individual spins, provides insight into the real-space fluctuations, revealing clusters of emerging order in the paramagnetic state, as well as collective short-range excitations in the ordered antiferromagnetic phase. Our understanding of this directional diffuse scattering in such a wide temperature range, both below and above TN , provides new insight into the magnetic phase transitions in classical frustrated systems.

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Arkadiy Simonov

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