Structure and elastic properties of Mg(OH)2_2 from density functional theory

The structure, lattice dynamics and mechanical properties of the magnesium hydroxide have been investigated with static density functional theory calculations as well as \it {ab initio} molecular dynamics. The hypothesis of a superstructure existing in the lattice formed by the hydrogen atoms has been tested. The elastic constants of the material have been calculated with static deformations approach and are in fair agreement with the experimental data. The hydrogen subsystem structure exhibits signs of disordered behaviour while maintaining correlations between angular positions of neighbouring atoms. We establish that the essential angular correlations between hydrogen positions are maintained to the temperature of at least 150 K and show that they are well described by a physically motivated probabilistic model. The rotational degree of freedom appears to be decoupled from the lattice directions above 30K

Observation of a molecular muonium polaron and its application to probing magnetic and electronic states

We thank the Engineering and Physical Sciences Research Council (EPSRC UK) for support via Grants No. EP/M000923/1, No. EP/K036408/1, No. EP/I004483/1, No. EP/S031081/1, and No. EP/S030263/1. L.L., S.S., D.J. and G.T. acknowledge also support from STFC-ISIS Neutron and Muon Source and Ada Lovelace Centre at STFC-SCD. We acknowledge use of the ARCHER (via the U.K. Car–Parrinello Consortium, EP/P022618/1 and EP/P022189/2), U.K. Materials and Molecular Modelling Hub (EP/P020194/1), and STFC Scientific Computing Department's SCARF HCP facilities. We acknowledge support from the Henry Royce Institute. This work was also supported financially through the EPSRC Grant Nos. EP/ P022464/1, and EP/R00661X/1.Muonium is a combination of first- and second-generation matter formed by the electrostatic interaction between an electron and an antimuon (μ+). Although a well-known physical system, their ability to form collective excitations in molecules had not been observed. Here, we give evidence for the detection of a muonium state that propagates in a molecular semiconductor lattice via thermally activated dynamics: a muonium polaron. By measuring the temperature dependence of the depolarization of the muonium state in C60, we observe a thermal narrowing of the hyperfine distribution that we attribute to the dynamics of the muonium between molecular sites. As a result of the time scale for muonium decay, the energies involved, charge and spin selectivity, this quasiparticle is a widely applicable experimental tool. It is an excellent probe of emerging electronic, dynamic, and magnetic states at interfaces and in low dimensional systems, where direct spatial probing is an experimental challenge owing to the buried interface, nanoscale elements providing the functionality localization and small magnitude of the effects.Publisher PDFPeer reviewe

Lattice dynamics of endotaxial silicide nanowires

Self-organized silicide nanowires are considered as main building blocks of future nanoelectronics and have been intensively investigated. In nanostructures, the lattice vibrational waves (phonons) deviate drastically from those in bulk crystals, which gives rise to anomalies in thermodynamic, elastic, electronic, and magnetic properties. Hence, a thorough understanding of the physical properties of these materials requires a comprehensive investigation of the lattice dynamics as a function of the nanowire size. We performed a systematic lattice dynamics study of endotaxial FeSi$_2$ nanowires, forming the metastable, surface-stabilized $\alpha$-phase, which are in-plane embedded into the Si(110) surface. The average widths of the nanowires ranged from 24 to 3 nm, their lengths ranged from several $\mu$m to about 100 nm. The Fe-partial phonon density of states, obtained by nuclear inelastic scattering, exhibits a broadening of the spectral features with decreasing nanowire width. The experimental data obtained along and across the nanowires unveiled a pronounced vibrational anisotropy that originates from the specific orientation of the tetragonal $\alpha$-FeSi$_2$ unit cell on the Si(110) surface. The results from first-principles calculations are fully consistent with the experimental data and allow for a comprehensive understanding of the lattice dynamics of endotaxial silicide nanowires.Comment: 9 pages, 7 figures, 3 table