Diffuse scattering in Ih ice

Wehinger, Björn; Chernyshov, Dmitry; Krisch, M.; Булат, С. А.; Ежов, В. Ф.; Bosak, Alexeï

doi:10.1088/0953-8984/26/26/265401

Cited by 21 publications

(22 citation statements)

References 32 publications

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“…Figure 1(a)i-(c)i shows water-ice, spin-ice, and orbital-ice scattering calculations, respectively. The results for water ice and spin ice are in good agreement with published calculations [3,49]. Calculations using the discrete Fourier transform and the FFT gave identical results, as required.…”

Section: Example Calculationssupporting

confidence: 85%

Ultrafast calculation of diffuse scattering from atomistic models

Paddison

2019

Acta Crystallogr A Found Adv

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Diffuse scattering is a rich source of information about disorder in crystalline materials, which can be modelled using atomistic techniques such as Monte Carlo and molecular dynamics simulations. Modern X‐ray and neutron scattering instruments can rapidly measure large volumes of diffuse‐scattering data. Unfortunately, current algorithms for atomistic diffuse‐scattering calculations are too slow to model large data sets completely, because the fast Fourier transform (FFT) algorithm has long been considered unsuitable for such calculations [Butler & Welberry (1992). J. Appl. Cryst.25, 391–399]. Here, a new approach is presented for ultrafast calculation of atomistic diffuse‐scattering patterns. It is shown that the FFT can actually be used to perform such calculations rapidly, and that a fast method based on sampling theory can be used to reduce high‐frequency noise in the calculations. These algorithms are benchmarked using realistic examples of compositional, magnetic and displacive disorder. They accelerate the calculations by a factor of at least 102, making refinement of atomistic models to large diffuse‐scattering volumes practical.

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Section: Example Calculationssupporting

confidence: 85%

Ultrafast calculation of diffuse scattering from atomistic models

Paddison

2019

Acta Crystallogr A Found Adv

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“…The pinch point Fig. 1 a is a type of singularity that is expected, and may be observed, in at least two types of system: firstly, dipolar systems, such as ferromagnets [1,2], and secondly, ice-rule systems, including hydrogen bonded ferroelectrics [3][4][5][6], water ice [7,8], spin ice [9][10][11][12][13][14], ionic ice [15,16], artificial spin ice [17][18][19], quantum spin ice [20][21][22] and antiferromagnetic spin liquids [23][24][25][26][27]. Such systems have the notable feature that they enter a highly correlated low-temperature state without any symmetry breaking.…”

Section: Introductionmentioning

confidence: 87%

Screening and the pinch point paradox in spin ice

Twengström

Henelius

Bramwell

2020

Phys. Rev. Research

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A pinch point singularity in the structure factor characterizes an important class of condensed matter that is a counterpoint to the paradigm of broken symmetry. This class includes water ice, charge ice and spin ice. Of these, dipolar spin ice affords the the pre-eminent model system because it has a well-established Hamiltonian, is simple enough to allow analytical theory and numerical simulation, and is well represented in experiment by Dy2Ti2O7 and Ho2Ti2O7. Nevertheless it is a considerable challenge to resolve the pinch points in simulation or experiment as they represent a very long range correlation. Here we present very high resolution simulations of the polarized neutron scattering structure factor of dipolar spin ice and new analytical theory of the pinch point profiles. We compare these with existing theory and experiment. We find that our simulations are consistent with theories that reveal the pinch points to be infinitely sharp, as a result of unscreened dipolar fields. However, neither simulation nor these theories are consistent with experiments, which instead is quantitatively captured by a theory that allows for screening of the dipolar fields and consequent strong broadening of the pinch points. This striking paradox is not easily resolved: broadening of the pinch points by random disorder seems to have been ruled out by existing theory, while deficiencies in the Hamiltonian description are not relevant. Intriguingly, we are left to consider the role of quantum fluctuations or the possibility of a fundamental correction to either the standard method of simulating dipolar systems, or the theory of polarized neutron scattering. More generally, our results may have relevance far beyond ice systems. For example, spin ice is a model Debye-Hückel (magnetic) electrolyte, so our basic observation that the screening length may diverge while the Debye length remains constant, may hint at a solution to the topical problem of 'underscreening' in concentrated ionic liquids.

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“…In what follows, we develop a theory of proton correlations in a classical model of ice Ih, neglecting all quantum tunnelling between different proton configurations. This theory provides a detailed and microscopically-derivable phenomenology to explain the diffuse scattering which is arises as a result of static proton disorder in ice Ih [48,49,55,[80][81][82][83][84][85][86][87].…”

Section: Proton Correlations In a Classical Model Of Ice Ihmentioning

confidence: 99%

Classical and quantum theories of proton disorder in hexagonal water ice

2016

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It has been known since the pioneering work of Bernal, Fowler and Pauling that common, hexagonal (Ih) water ice is the archetype of a frustrated material : a proton-bonded network in which protons satisfy strong local constraints -the "ice rules" -but do not order. While this proton disorder is well established, there is now a growing body of evidence that quantum effects may also have a role to play in the physics of ice at low temperatures. In this Article we use a combination of numerical and analytic techniques to explore the nature of proton correlations in both classical and quantum models of ice Ih. In the case of classical ice Ih, we find that the ice rules have two, distinct, consequences for scattering experiments -singular "pinch points", reflecting a zero-divergence condition on the uniform polarization of the crystal, and broad, asymmetric features, coming from its staggered polarisation. In the case of the quantum model, we find that the collective quantum tunnelling of groups of protons can convert states obeying the ice rules into a quantum liquid, whose excitations are birefringent, emergent photons. We make explicit predictions for scattering experiments on both classical and quantum ice Ih, and show how the quantum theory can explain the "wings" of incoherent inelastic scattering observed in recent neutron scattering experiments [Bove et al., Phys. Rev. Lett. 103, 165901 (2009)]. These results raise the intriguing possibility that the protons in ice Ih could form a quantum liquid at low temperatures, in which protons are not merely disordered, but continually fluctuate between different configurations obeying the ice rules.

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Diffuse scattering in Ih ice

Cited by 21 publications

References 32 publications

Ultrafast calculation of diffuse scattering from atomistic models

Ultrafast calculation of diffuse scattering from atomistic models

Screening and the pinch point paradox in spin ice

Classical and quantum theories of proton disorder in hexagonal water ice

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