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Softening of a flat phonon mode in the kagome ScV 6Sn 6. Nat Commun 2023; 14:6646. [PMID: 37863907 PMCID: PMC10589229 DOI: 10.1038/s41467-023-42186-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 09/29/2023] [Indexed: 10/22/2023] Open
Abstract
Geometrically frustrated kagome lattices are raising as novel platforms to engineer correlated topological electron flat bands that are prominent to electronic instabilities. Here, we demonstrate a phonon softening at the kz = π plane in ScV6Sn6. The low energy longitudinal phonon collapses at ~98 K and q = [Formula: see text] due to the electron-phonon interaction, without the emergence of long-range charge order which sets in at a different propagation vector qCDW = [Formula: see text]. Theoretical calculations corroborate the experimental finding to indicate that the leading instability is located at [Formula: see text] of a rather flat mode. We relate the phonon renormalization to the orbital-resolved susceptibility of the trigonal Sn atoms and explain the approximately flat phonon dispersion. Our data report the first example of the collapse of a kagome bosonic mode and promote the 166 compounds of kagomes as primary candidates to explore correlated flat phonon-topological flat electron physics.
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Order-disorder charge density wave instability in the kagome metal (Cs,Rb)V 3Sb 5. Nat Commun 2023; 14:1015. [PMID: 36823175 PMCID: PMC9950456 DOI: 10.1038/s41467-023-36668-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Accepted: 02/06/2023] [Indexed: 02/25/2023] Open
Abstract
The origin of the charge density wave phases in the kagome metal compound AV3Sb5 is still under great scrutiny. Here, we combine diffuse and inelastic x-ray scattering to identify a 3-dimensional precursor of the charge order at the L point that condenses into a CDW through a first order phase transition. The quasi-elastic critical scattering indicates that the dominant contribution to the diffuse precursor is the elastic central peak without phonon softening. However, the inelastic spectra show a small broadening of the Einstein-type phonon mode on approaching TCDW. Our results point to the situation where the Fermi surface instability at the L point is of order-disorder type with critical growth of quasi-static domains. The experimental data indicate that the CDW consists on an alternating Star of David and trihexagonal distortions and its dynamics goes beyond the classical weak-coupling scenario and is discussed within strong-electron phonon coupling and non-adiabatic models.
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Soft-Phonon and Charge-Density-Wave Formation in Nematic BaNi_{2}As_{2}. PHYSICAL REVIEW LETTERS 2022; 129:247602. [PMID: 36563274 DOI: 10.1103/physrevlett.129.247602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2022] [Revised: 10/14/2022] [Accepted: 11/21/2022] [Indexed: 06/17/2023]
Abstract
We use diffuse and inelastic x-ray scattering to study the formation of an incommensurate charge-density-wave (I-CDW) in BaNi_{2}As_{2}, a candidate system for charge-driven electronic nematicity. Intense diffuse scattering is observed around the modulation vector of the I-CDW, Q_{I-CDW}. It is already visible at room temperature and collapses into superstructure reflections in the long-range ordered state where a small orthorhombic distortion occurs. A clear dip in the dispersion of a low-energy transverse optical phonon mode is observed around Q_{I-CDW}. The phonon continuously softens upon cooling, ultimately driving the transition to the I-CDW state. The transverse character of the soft-phonon branch elucidates the complex pattern of the I-CDW satellites observed in the current and earlier studies and settles the debated unidirectional nature of the I-CDW. The phonon instability and its reciprocal space position are well captured by our ab initio calculations. These, however, indicate that neither Fermi surface nesting, nor enhanced momentum-dependent electron-phonon coupling can account for the I-CDW formation, demonstrating its unconventional nature.
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Symmetry breaking and short-range order in aperiodic urea inclusion crystals. ACTA CRYSTALLOGRAPHICA SECTION A FOUNDATIONS AND ADVANCES 2022. [DOI: 10.1107/s2053273322095511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
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5
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Pauflerite β-VOSO 4 as a 1D S = 1/2 Heisenberg antiferromagnetic system: crystal structure, disorder and thermal expansivity. ACTA CRYSTALLOGRAPHICA SECTION A FOUNDATIONS AND ADVANCES 2022. [DOI: 10.1107/s2053273322095274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
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6
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Structural complexity in the RP phase La 2CoO 4+δ explored by synchrotron X-ray single-crystal diffraction and neutron powder diffraction. ACTA CRYSTALLOGRAPHICA SECTION A FOUNDATIONS AND ADVANCES 2022. [DOI: 10.1107/s2053273322094360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
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7
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Strain wave pathway to semiconductor-to-metal transition revealed by time-resolved X-ray powder diffraction. Nat Commun 2021; 12:1239. [PMID: 33623010 PMCID: PMC7902810 DOI: 10.1038/s41467-021-21316-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 01/13/2021] [Indexed: 11/09/2022] Open
Abstract
One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable Ti3O5 nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed Ti3O5 surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.
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Four new Ophiostoma species associated with conifer- and hardwood-infesting bark and ambrosia beetles from the Czech Republic and Poland. Antonie Van Leeuwenhoek 2019; 112:1501-1521. [PMID: 31140027 PMCID: PMC6748885 DOI: 10.1007/s10482-019-01277-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 05/14/2019] [Indexed: 12/24/2022]
Abstract
Fungi under the order Ophiostomatales (Ascomycota) are known to associate with various species of bark beetles (Coleoptera: Curculionidae: Scolytinae). In addition this group of fungi contains many taxa that can impart blue-stain on sapwood and some are important tree pathogens. A recent survey that focussed on the diversity of the Ophiostomatales in the forest ecosystems of the Czech Republic and Poland uncovered four putative new species. Phylogenetic analyses of four gene regions (ITS1-5.8S-ITS2 region, ß-tubulin, calmodulin, and translation elongation factor 1-α) indicated that these four species are members of the genus Ophiostoma. All four newly described species can be distinguished from each other and from closely related species based on DNA sequence comparisons, morphological characters, growth rates, and their insect associations. Based on this study four new taxa can be circumscribed and the following names are provided: Ophiostoma pityokteinis sp. nov., Ophiostoma rufum sp. nov., Ophiostoma solheimii sp. nov., and Ophiostoma taphrorychi sp. nov. O. rufum sp. nov. is a member of the Ophiostoma piceae species complex, while O. pityokteinis sp. nov. resides in a discrete lineage within Ophiostoma s. stricto. O. taphrorychi sp. nov. together with O. distortum formed a well-supported clade in Ophiostoma s. stricto close to O. pityokteinis sp. nov. O. solheimii sp. nov. groups within a currently undefined lineage A, which also includes Ophiostoma grandicarpum and Ophiostoma microsporum. This study highlights the need for more intensive surveys that should include additional countries of Central Europe, insect vectors and host tree species in order to elucidate Ophiostoma species diversity in this region.
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Uniaxial pressure control of competing orders in a high-temperature superconductor. Science 2019; 362:1040-1044. [PMID: 30498124 DOI: 10.1126/science.aat4708] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 10/25/2018] [Indexed: 11/02/2022]
Abstract
Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa2Cu3O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials.
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Abstract
Ammonium oxofluorotitanate, NH4TiOF3, is probably the best known precursor for the synthesis of anatase mesocrystals. Transformation of NH4TiOF3 into TiO2 through thermal decomposition, accompanied by hydrolysis, preserves some structural features of the precursor. Currently, any discussion of the mechanism of this transformation is difficult, as the exact crystal structure of the starting compound is not available and no intermediate structures are known. This article describes the outcome of single-crystal and powder X-ray diffraction studies, revealing the existence of two polymorphs of the parent NH4TiOF3 at different temperatures. A second-order phase transition from the polar Pca21 α phase (1), stable at room temperature, to the Pma2 β phase (2) above ∼433 K has been demonstrated. The direction of the pseudo-fourfold axis in NH4TiOF3 coincides with the orientation of the fourfold axis of anatase mesocrystals, consistent with a topotactical transformation.
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A new diffractometer for diffuse scattering studies on the ID28 beamline at the ESRF. JOURNAL OF SYNCHROTRON RADIATION 2019; 26:272-279. [PMID: 30655495 DOI: 10.1107/s1600577518016132] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Accepted: 11/14/2018] [Indexed: 06/09/2023]
Abstract
A new diffractometer is now available to the general user community at the ESRF. The new diffractometer is a side station of the high-resolution inelastic X-ray scattering spectrometer on beamline ID28 and is located in the same experimental hutch. Both instruments can be operated simultaneously. The new diffractometer combines a fast and low-noise hybrid pixel detector with a variable diffraction geometry. The beam spot on the sample is 50 µm × 50 µm, where focusing is achieved by a combination of Be lenses and a KB mirror. Wavelengths from 0.5 to 0.8 Å can be used for the diffraction experiments. The setup is compatible with a variety of sample environments, allowing studies under non-ambient conditions. The diffractometer is optimized to allow a rapid survey of reciprocal space and diffuse scattering for the identification of regions of interest for subsequent inelastic scattering studies, but can also be employed as a fully independent station for structural studies from both powder and single-crystal diffraction experiments. Several software packages for the transformation and visualization of diffraction data are available. An analysis of data collected with the new diffractometer shows that the ID28 side station is a state-of-the-art instrument for structural investigations using diffraction and diffuse scattering experiments.
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Erratum: Lattice Dynamics of EuO: Evidence for Giant Spin-Phonon Coupling [Phys. Rev. Lett. 116, 185501 (2016)]. PHYSICAL REVIEW LETTERS 2017; 119:079903. [PMID: 28949658 DOI: 10.1103/physrevlett.119.079903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Indexed: 06/07/2023]
Abstract
This corrects the article DOI: 10.1103/PhysRevLett.116.185501.
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Lattice Dynamics of EuO: Evidence for Giant Spin-Phonon Coupling. PHYSICAL REVIEW LETTERS 2016; 116:185501. [PMID: 27203332 DOI: 10.1103/physrevlett.116.185501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Indexed: 06/05/2023]
Abstract
Comprehensive studies of lattice dynamics in the ferromagnetic semiconductor EuO have been performed by a combination of inelastic x-ray scattering, nuclear inelastic scattering, and ab initio calculations. A remarkably large broadening of the transverse acoustic phonons was discovered at temperatures above and below the Curie temperature T_{C}=69 K. This result indicates a surprisingly strong momentum-dependent spin-phonon coupling induced by the spin dynamics in EuO.
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A device for the application of uniaxial strain to single crystal samples for use in synchrotron radiation experiments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:103904. [PMID: 26520968 DOI: 10.1063/1.4933383] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present the design, construction, and testing of a straining device compatible with many different synchrotron radiation techniques, in a wide range of experimental environments (including low temperature, high field and ultra-high vacuum). The device has been tested by X-ray diffraction on single crystal samples of quasi-one-dimensional Cs2Mo6Se6 and K2Mo6Se6, in which microscopic strains up to a Δc/c = 0.12% ± 0.01% change in the c lattice parameters have been achieved. We have also used the device in an inelastic X-ray scattering experiment, to probe the strain-dependent speed of sound ν along the c axis. A reduction Δν/ν of up to -3.8% was obtained at a strain of Δc/c = 0.25% in K2Mo6Se6.
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Localization of propagative phonons in a perfectly crystalline solid. PHYSICAL REVIEW LETTERS 2014; 113:025506. [PMID: 25062208 DOI: 10.1103/physrevlett.113.025506] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Indexed: 06/03/2023]
Abstract
Perfectly crystalline solids are excellent heat conductors. Prominent counterexamples are intermetallic clathrates, guest-host systems with a high potential for thermoelectric applications due to their ultralow thermal conductivities. Our combined experimental and theoretical investigation of the lattice dynamics of a particularly simple binary representative, Ba(8)Si(46), identifies the mechanism responsible for the reduction of lattice thermal conductivity intrinsic to the perfect crystal structure. Above a critical wave vector, the purely harmonic guest-host interaction leads to a drastic transfer of spectral weight to the guest atoms, corresponding to a localization of the propagative phonons.
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Role of disorder in the thermodynamics and atomic dynamics of glasses. PHYSICAL REVIEW LETTERS 2014; 112:025502. [PMID: 24484025 DOI: 10.1103/physrevlett.112.025502] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Indexed: 06/03/2023]
Abstract
We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO2. The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higher-density crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal.
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Suppression of thermal conductivity by rattling modes in thermoelectric sodium cobaltate. NATURE MATERIALS 2013; 12:1028-1032. [PMID: 23975057 DOI: 10.1038/nmat3739] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 07/24/2013] [Indexed: 06/02/2023]
Abstract
The need for both high electrical conductivity and low thermal conductivity creates a design conflict for thermoelectric systems, leading to the consideration of materials with complicated crystal structures. Rattling of ions in cages results in low thermal conductivity, but understanding the mechanism through studies of the phonon dispersion using momentum-resolved spectroscopy is made difficult by the complexity of the unit cells. We have performed inelastic X-ray and neutron scattering experiments that are in remarkable agreement with our first-principles density-functional calculations of the phonon dispersion for thermoelectric Na(0.8)CoO2, which has a large-period superstructure. We have directly observed an Einstein-like rattling mode at low energy, involving large anharmonic displacements of the sodium ions inside multi-vacancy clusters. These rattling modes suppress the thermal conductivity by a factor of six compared with vacancy-free NaCoO2. Our results will guide the design of the next generation of materials for applications in solid-state refrigerators and power recovery.
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Intrinsic crystal phase separation in the antiferromagnetic superconductor Rb(y)Fe(2-x)Se2: a diffraction study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:435701. [PMID: 23032696 DOI: 10.1088/0953-8984/24/43/435701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The crystal and magnetic structures of the superconducting iron-based chalcogenides Rb(y)Fe(2-x)Se(2) have been studied by means of single-crystal synchrotron x-ray and high-resolution neutron powder diffraction in the temperature range 2-570 K. The ground state of the crystal is an intrinsically phase-separated state with two distinct-by-symmetry phases. The main phase has the iron vacancy ordered √5 × √5 superstructure (I4/m space group) with AFM ordered Fe spins. The minority phase does not have √5 × √5-type of ordering and has a smaller in-plane lattice constant a and larger tetragonal c-axis and can be well described by assuming the parent average vacancy disordered structure (I4/mmm space group) with the refined stoichiometry Rb(0.60(5))(Fe(1.10(5))Se)(2). The minority phase amounts to 8-10% mass fraction. The unit cell volume of the minority phase is 3.2% smaller than the one of the main phase at T = 2 K and has quite different temperature dependence. The minority phase merges with the main vacancy ordered phase on heating above the phase separation temperature T(P) = 475 K. The spatial dimensions of the phase domains strongly increase above T(P) from 1000 to >2500 Å due to the integration of the regions of the main phase that were separated by the second phase at low temperatures. Additional annealing of the crystals at a temperature T = 488 K, close to T(P), for a long time drastically reduces the amount of the minority phase.
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Structural heterogeneity and diffuse scattering in morphotropic lead zirconate-titanate single crystals. PHYSICAL REVIEW LETTERS 2012; 109:097603. [PMID: 23002887 DOI: 10.1103/physrevlett.109.097603] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Indexed: 06/01/2023]
Abstract
Complementary diffuse and inelastic synchrotron x-ray scattering measurements of lead zirconate-titanate single crystals with composition near the morphotropic phase boundary (x=0.475) are reported. In the temperature range 293 K<T<400 K a highly anisotropic quasielastic diffuse scattering is observed. Above 400 K this scattering disappears. Its main features can be reproduced by the model of inhomogeneous lattice deformations caused by inclusions of a tetragonal phase into a rhombohedral or monoclinic phase. This observation supports the idea that PZT at its morphotropic phase boundary is essentially structurally inhomogeneous.
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Three-dimensional mapping of reciprocal space and structural complexity of AxFe 2−ySe 2superconductors ( A= Rb, Cs). Acta Crystallogr A 2012. [DOI: 10.1107/s0108767312096389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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21
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Inelastic X-ray scattering: phonon spectroscopy under the extreme conditions. Acta Crystallogr A 2012. [DOI: 10.1107/s010876731209811x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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22
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Lattice dynamics and superconductivity in cerium at high pressure. PHYSICAL REVIEW LETTERS 2012; 108:045502. [PMID: 22400861 DOI: 10.1103/physrevlett.108.045502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Revised: 12/01/2011] [Indexed: 05/31/2023]
Abstract
We have measured phonon dispersion relations of the high-pressure phase cerium-oC4 (α' phase with the α-uranium crystal structure) at 6.5 GPa by using inelastic x-ray scattering. Pronounced phonon anomalies are observed, which are remarkably similar to those of α-U. First-principles electronic structure calculations reproduce the anomalies and allow us to identify strong electron-phonon coupling as their origin. At the low-pressure end of its stability range, Ce-oC4 is on the verge of a lattice-dynamical instability and possibly a charge density wave. The superconducting transition temperatures of the fcc, oC4, and mC4 phases of Ce have been calculated, and the superconductivity observed experimentally by Wittig and Probst is attributed to the oC4 phase.
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Diffuse scattering in relaxor ferroelectrics: true three-dimensional mapping, experimental artefacts and modelling. Acta Crystallogr A 2011; 68:117-23. [DOI: 10.1107/s0108767311040281] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 09/29/2011] [Indexed: 11/10/2022] Open
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Equivalence of the boson peak in glasses to the transverse acoustic van Hove singularity in crystals. PHYSICAL REVIEW LETTERS 2011; 106:225501. [PMID: 21702612 DOI: 10.1103/physrevlett.106.225501] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Indexed: 05/31/2023]
Abstract
We compare the atomic dynamics of the glass to that of the relevant crystal. In the spectra of inelastic scattering, the boson peak of the glass appears higher than the transverse acoustic (TA) singularity of the crystal. However, the density of states shows that they have the same number of states. Increasing pressure causes the transformation of the boson peak of the glass towards the TA singularity of the crystal. Once corrected for the difference in the elastic medium, the boson peak matches the TA singularity in energy and height. This suggests the identical nature of the two features.
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InN thin film lattice dynamics by grazing incidence inelastic x-ray scattering. PHYSICAL REVIEW LETTERS 2011; 106:205501. [PMID: 21668242 DOI: 10.1103/physrevlett.106.205501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Indexed: 05/30/2023]
Abstract
Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine the complete elastic stiffness tensor, the acoustic and low-energy optic phonon dispersion relations of thin wurtzite indium nitride films. Indium nitride is an especially relevant example, due to the technological interest for optoelectronic and solar cell applications in combination with other group III nitrides.
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Abstract
ABSTRACTThis paper is a survey of recent author's results obtained by the authors. It shows that many oxides can be obtained as thin epitaxial films in spite of their thermodynamic instability in bulk state at the film deposition conditions. This new synthetic approach, named epitaxial stabilization, is based on free energy gain due to structural coherence at the film/substrate interface. The epitaxial stabilization can be effectively used to enlarge the spectrum of new functional materials.
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Spin Crossover in Ferropericlase at High Pressure: A Seismologically Transparent Transition? Science 2011; 331:64-7. [DOI: 10.1126/science.1198429] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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3D imaging of the Fermi surface by thermal diffuse scattering. PHYSICAL REVIEW LETTERS 2009; 103:076403. [PMID: 19792668 DOI: 10.1103/physrevlett.103.076403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Indexed: 05/28/2023]
Abstract
We use thermal diffuse scattering of x rays to visualize the lens-shaped portions of the Fermi surface in metallic zinc. Our interpretation of the nature of the observed scattered intensity anomalies is supported by the incorporation of inelastic x-ray scattering measurements as well as ab initio calculations of the electronic structure and lattice dynamics. Our work demonstrates that thermal diffuse scattering complements well-established techniques and is a powerful tool in its own right for studying the shape of the Fermi surface through the associated electron-phonon coupling.
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Origin of the incommensurate modulation in Te-III and fermi-surface nesting in a simple metal. PHYSICAL REVIEW LETTERS 2009; 102:035501. [PMID: 19257366 DOI: 10.1103/physrevlett.102.035501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Indexed: 05/27/2023]
Abstract
Inelastic x-ray scattering experiments have been performed on incommensurately modulated Te-III at high pressure and reveal a pronounced phonon anomaly. The anomaly is reproduced in first-principles lattice dynamics calculations of unmodulated, body-centered monoclinic (bcm) Te, which is shown to be dynamically unstable. The calculated Fermi surface of bcm Te exhibits surprisingly effective nesting for a simple, electronically three-dimensional metal. The combined experimental and theoretical results corroborate recent proposals that the modulated crystal structure of Te-III and other chalcogens is the manifestation of a pressure-induced charge-density wave state.
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Vibrational properties of hexagonal boron nitride: inelastic X-ray scattering and ab initio calculations. PHYSICAL REVIEW LETTERS 2007; 98:095503. [PMID: 17359168 DOI: 10.1103/physrevlett.98.095503] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Indexed: 05/05/2023]
Abstract
The phonon dispersion relations of bulk hexagonal boron nitride have been determined from inelastic x-ray scattering measurements and analyzed by ab initio calculations. Experimental data and calculations show an outstanding agreement and reconcile the controversies raised by recent experimental data obtained by electron-energy loss spectroscopy and second-order Raman scattering.
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Abstract
OBJECTIVE To determine whether patients with Parkinson's disease who are enrolled in a resistance training program can gain strength similar to that of normal control subjects and whether these gains in strength would improve their gait function. DESIGN Subjects included 14 patients with mild-to-moderate Parkinson's disease of either gender and six normal control subjects of similar age. The training consisted of an 8-wk course of resistance training twice per week, focused primarily on the lower limbs. The primary outcome measures consisted of exercise performance monitoring and quantitative gait analysis before and after the training course. RESULTS Both the patients with Parkinson's disease and normal control subjects significantly increased their performance with resistance training. Subjects with Parkinson's disease had gains in strength similar to those of normal elderly adults. Patients with Parkinson's disease also had significant gains in stride length, walking velocity, and postural angles compared with pretreatment values. CONCLUSIONS Patients with mild-to-moderate Parkinson's disease can obtain increases in performance or strength similar to that of normal adults of the same age in a resistance training program. Resistance training can produce functional improvements in gait and may, therefore, be useful as part of a physical rehabilitation and/or health maintenance program for patients with Parkinson's disease.
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Standard osteopathic manipulative treatment acutely improves gait performance in patients with Parkinson's disease. THE JOURNAL OF THE AMERICAN OSTEOPATHIC ASSOCIATION 1999; 99:92-8. [PMID: 10079641 DOI: 10.7556/jaoa.1999.99.2.92] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Patients with Parkinson's disease exhibit a variety of motor deficits which can ultimately result in complete disability. The primary objective of this study was to quantitatively evaluate the effect of osteopathic manipulative treatment (OMT) on the gait of patients with Parkinson's disease. Ten patients with idiopathic Parkinson's disease and a group of eight age-matched normal control subjects were subjected to an analysis of gait before and after a single session of an OMT protocol. A separate group of 10 patients with Parkinson's disease was given a sham-control procedure and tested in the same manner. In the treated group of patients with Parkinson's disease, statistically significant increases were observed in stride length, cadence, and the maximum velocities of upper and lower extremities after treatment. There were no significant differences observed in the control groups. The data demonstrate that a single session of an OMT protocol has an immediate impact on Parkinsonian gait. Osteopathic manipulation may be an effective physical treatment method in the management of movement deficits in patients with Parkinson's disease.
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Establishment of behavioral parameters for the evaluation of osteopathic treatment principles in a rat model of arthritis. THE JOURNAL OF THE AMERICAN OSTEOPATHIC ASSOCIATION 1997; 97:207-14. [PMID: 9154739 DOI: 10.7556/jaoa.1997.97.4.207] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Unilateral arthritis was produced in rats by use of methylated bovine serum albumin in a model of antigen-induced arthritis. The progression of arthritis was measured by computerized motion analysis, bilateral joint circumference, voluntary extension force of the hindlegs, and length of ankle extension. Animals with induced arthritis were assigned to treated and untreated groups on the basis of approximately equal deficits by the parameters measured. A third group of rats, which did not have arthritis induced and received no treatment, served to establish mean normal parameters. Modified techniques of muscle energy, passive movement of the ankle and knee, and passive myofascial stretch were applied to the animals, and the animals were exercised in a mechanized exercise wheel. Parameters associated with gait were examined by computerized motion analysis of walking. Animals treated with manipulation and exercise improved significantly relative to untreated animals with antigen-induced arthritis in vertical ankle lift, ankle-based and foot-based stride lengths, knee circumference, and normalized extension of the ankle. The results demonstrate that the parameters identified can be used to detect functional deficits and significant improvement from those deficits can be derived from a nonpharmacologic treatment paradigm that includes osteopathic manipulation and exercise in an animal model of arthritis. These parameters may be useful in the identification of the relative benefits of independent treatment variables including frequency of osteopathic manipulation and exercise and the relative benefits of each in this model. Also, they may elucidate how these treatments produce their beneficial effects clinically.
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