A5029210156- Rare-earth and actinide compounds
- Muon and positron interactions and applications
- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Advanced Chemical Physics Studies
- Inorganic Chemistry and Materials
- Magnetic Properties of Alloys
- Electronic and Structural Properties of Oxides
- Organic and Molecular Conductors Research
- Magnetic properties of thin films
- High-pressure geophysics and materials
- Nuclear physics research studies
- Nuclear Physics and Applications
- Atomic and Molecular Physics
- Solid-state spectroscopy and crystallography
- Quantum and electron transport phenomena
- Surface and Thin Film Phenomena
- Copper Interconnects and Reliability
- Graphene research and applications
- Boron and Carbon Nanomaterials Research
- Quantum, superfluid, helium dynamics
- Intermetallics and Advanced Alloy Properties
- Superconductivity in MgB2 and Alloys
University of Bristol
2014-2024
Bristol Robotics Laboratory
1996-2011
Harbin Institute of Technology
2011
University of Geneva
1997-2001
The charge density wave transition is investigated in the bilayer family of rare-earth tritelluride $R{\mathrm{Te}}_{3}$ compounds ($R=\mathrm{Sm}$, Gd, Tb, Dy, Ho, Er, and Tm) via high-resolution x-ray diffraction electrical resistivity. temperature increases monotonically with increasing lattice parameter from $244(3)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $\mathrm{Tm}{\mathrm{Te}}_{3}$ to $416(3)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $\mathrm{Sm}{\mathrm{Te}}_{3}$. heaviest members...
We present a detailed angle-resolved photoemission spectroscopy (ARPES) investigation of the $R{\text{Te}}_{3}$ family, which sets this system as an ideal ``textbook'' example for formation nesting driven charge density wave (CDW). This family indeed exhibits full range phenomena that can be associated to CDW instabilities, from opening large gaps on best nested parts Fermi surface (up 0.4 eV), existence residual metallic pockets. ARPES is suited technique characterize these features, thanks...
The Fermi surface of rare-earth tri-tellurides ({\it R}Te$_{3}$) is investigated in terms the nesting driven charge-density wave formation using positron annihilation and first-principles LMTO calculations. revealed as a strong candidate for driving these compounds. vector obtained from experiments on GdTe$_{3}$ determined to be ${\mathbf q} = (0.28\pm0.02,0,0) {\mathbf a}^{*}$, (${\mathbf a}^{*}=2\pi/{\mathbf a}$), excellent agreement with previous experimental theoretical studies.
The concept of the Fermi surface is at very heart our understanding metallic state. Displaying intricate and often complicated shapes, surfaces real metals are both aesthetically beautiful subtly powerful. A range examples presented startling array physical phenomena whose origin can be traced to shape surface, together with experimental observations particular features.
The rare earth nickel borocarbides, with the generic formula $R$Ni$_{2}$B$_{2}$C, have recently been shown to display a rich variety of phenomena. Most striking has competition between, and even coexistence of, antiferromagnetism superconductivity. We measured Fermi surface (FS) LuNi$_{2}$B$_{2}$C, that it possesses nesting features capable explaining some phenomena experimentally observed. In particular, had previously conjectured particular sheet FS is responsible for modulated magnetic...
The electronic structure, Fermi surface and elastic properties of the iso-structural iso-electronic LaSn$_3$ YSn$_3$ intermetallic compounds are studied under pressure within framework density functional theory including spin-orbit coupling. consists two sheets, which second is very complex. Under a third sheet appears around compression $V/V_0=0.94$, while small topology change in seen at $V/V_0=0.90$. This may be accordance with anomalous behaviour superconducting transition temperature...
The results of positron-annihilation lifetime spectroscopy measurements on undoped, electron-irradiated, and Nb-doped ${\text{SrTiO}}_{3}$ single crystals are reported. Perfect lattice vacancy defect positron lifetimes were calculated using two different first-principles schemes. Sr-vacancy defect-related was obtained from Nb-doped, vacuum-annealed samples. Undoped showed a component dominated by trapping to Ti vacancy-related defects.
We show that the Fermi surface can survive presence of extreme compositional disorder in equiatomic alloy Ni_{0.25}Fe_{0.25}Co_{0.25}Cr_{0.25}. Our high-resolution Compton scattering experiments reveal a which is smeared across significant fraction Brillouin zone (up to 40% 2π/a). The extent this smearing and its variation on between different sheets have been determined, estimates electron mean free path residual resistivity made by connecting with coherence length quasiparticle states.
The electronic structure of the newly discovered superconducting perovskite ${\mathrm{MgCNi}}_{3}$ is calculated using LMTO method. states near Fermi energy are found to be dominated by $\mathrm{Ni}\ensuremath{-}d.$ Stoner factor low while electron-phonon coupling constant estimated about 0.5, which suggests that material a conventional type superconductor where ${T}_{c}$ not affected magnetic interactions. However, proximity large peak in density conjunction with reported nonstoichiometry...
The first measurement of both the size and shape region Fermi surface yttrium known as ``webbing'' is reported. This particular feature considerable interest because it very similar to that found in a number heavier rare earth metals, where believed play vital role driving exotic magnetic structures therein. In this positron study, two-dimensional angular correlation measurements combined with three-dimensional reconstruction provide direct image part surface.
First-principles calculations of the electronic structure members $R{\text{NiC}}_{2}$ series are presented and their Fermi surfaces investigated for nesting propensities, which might be linked to charge-density waves exhibited by certain ($R=\text{Sm}$, Gd, Nd). Calculations generalized susceptibility, ${\ensuremath{\chi}}_{0}(\mathbf{q},\ensuremath{\omega})$, show strong peaks at same $\mathbf{q}$ vector in both real imaginary parts these compounds. Moreover, this peak occurs a wave is very...
The Fermi surface of the ferromagnetic shape-memory alloy Ni2MnGa has been determined experimentally with two-dimensional angular correlation electron–positron annihilation radiation. Our results are supported by first principles electronic structure calculations. measured electron occupancy within Brillouin zone is consistent existence two nesting features present in surfaces calculated previous studies. vectors match modulation pre-martensitic intermediate and that martensitic structure.
Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst frustration is observed in numerous electrically insulating systems, metals it a rare phenomenon. The interplay of itinerant conduction electrons mediating between localised moments strong spin-orbit coupling likely fundamental these systems. Therefore, knowledge the precise shape and topology Fermi surface important any explanation behaviour....
Magnetic Compton scattering, x-ray magnetic circular dichroism spectroscopy, and bulk magnetometry measurements are performed on a set of medium- (NiFeCo NiFeCoCr) high-entropy (NiFeCoCrPd NiFeCoCrMn) Cantor-Wu alloys. The spin momentum densities determined by scattering remarkably isotropic, this is consequence the smearing electronic structure disorder electron quasiparticles. Nonzero signals observed for every element in alloy indicating differences populations majority minority states...
We report a study of the spin moment in single crystal Nb${}_{(1\ensuremath{-}y)}$Fe${}_{(2+y)}$ with $y=0.015$ using spin-dependent Compton scattering conjunction ab initio electronic structure calculations. From experiment, we find that total is $0.245\ifmmode\pm\else\textpm\fi{}0.004{\ensuremath{\mu}}_{B}$. Comparison measured density theoretical results from linearized muffin-tin orbital calculations determines there to be ferrimagnetic arrangement Fe moments, 2$a$ site aligned...
The effect of dimensionality on materials properties has become strikingly evident with the recent discovery graphene. Charge ordering phenomena can be induced in one dimension by periodic distortions a material's crystal structure, termed Peierls transition. Charge-density waves also solids strong Coulomb repulsion between carriers, and at extreme limit, Wigner predicted that crystallization itself an electrons gas free space close to absolute zero temperature. Similar are observed higher...
The recent discovery of superconductivity coexisting with weak itinerant ferromagnetism in the d-electron intermetallic compound ZrZn2 strongly suggests spin-fluctuation mediated superconductivity. Ab initio electronic structure calculations Fermi surface and generalized susceptibilities are performed to investigate viability longitudinal spin-fluctuation-induced spin-triplet ferromagnetic state. critical temperature is estimated be order 1 K. Additionally, it shown that spite a strong...
The first direct experimental evidence to suggest the Fermi surface (FS) as being responsible for driving helical antiferromagnetic ordering in a gadolinium-yttrium alloy is reported. presence of FS sheet capable nesting revealed, and vector associated with found be excellent agreement periodicity ordering.
Positron lifetime spectroscopy has been applied to estimate the free volume hole size distribution in polycarbonate (PC) and polystyrene (PS) at room temperature. The radius density distributions are determined from ortho-positronium obtained via a Laplace inversion of measured positron spectra. number holes estimated distributions. All may be well approximated by single Gaussians. have centres 〈rf〉 〈vfn〉 0.29 nm 0.1 nm3 PC, 0.28 0.09 PS. FWHM corresponding 0.042 0.040 (PC), 0.039 0.34 (PS),...
The Fermi surface topology of the shape-memory alloy ${\mathrm{Ni}}_{0.62}{\mathrm{Al}}_{0.38}$ has been determined using Compton scattering. A large area this can be made to nest with other areas by translation through a vector $\ensuremath{\approx}0.18[1,1,0](2\ensuremath{\pi}/a)$, which corresponds wave associated martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these are driven...
The state-dependence of the enhancement electron-positron momentum density is investigated for some transition and simple metals (Cr, V, Ag Al). Quantitative comparison with linearized muffin-tin orbital calculations corresponding quantity in first Brillouin zone shown to yield a measurement s, p d states, independent any parameterizations terms electron local positron. An empirical correction that can be applied first-principles state-dependent model proposed reproduces measured very well,...
The electronic structures, densities of states, Fermi surfaces and elastic properties AB3 (A =La, Y; B =Pb, In, Tl) compounds are studied under pressure using the full-potential linear augmented plane wave (FP-LAPW) method within local density approximation for exchange–correlation functional including spin–orbit coupling. surface topology changes found all isostructural compression (at V/V0 = 0.90 LaPb3 (pressure 8 GPa), at 0.98 AIn3 1.5 0.80 ATl3 in excess 18 GPa)) apart from YPb3,...
The strength of the electron-phonon coupling parameter and its evolution throughout a solid's phase diagram often determines phenomena such as superconductivity, charge- spin-density waves. Its experimental determination relies on ability to distinguish thermally activated phonons from those emitted by conduction band electrons, which can be achieved in an elegant way ultrafast techniques. Separating electronic out-of-equilibrium lattice subsystems, we probed their re-equilibration...