Inelastic Neutron-scattering Experiments Research Articles

Finite temperature calculations on spin correlation functions of the Haldane gap compound

Abstract We present the finite temperature calculations on the spin correlation functions of the Haldane gap compound CsNiCl 3 . Based on the coupled-chain theory, two methods are used to do the calculations: the large- N expansion and the Ginzburg–Landau approach. The comparisons with the inelastic neutron-scattering experiments are discussed.

Dynamical properties and temperature induced molecular disordering ofLiBH4andLiBD4

We report on neutron powder-diffraction experiments, inelastic incoherent neutron-scattering experiments, and density-functional calculations on dynamics, order and disorder properties of ${\text{LiBH}}_{4}$ and ${\text{LiBD}}_{4}$. From refinement of ${\text{LiBD}}_{4}$ structure at 10 and 302 K, we found an almost ideal tetrahedral geometry of ${\text{BD}}_{4}$ ions (difference between shortest and longest interatomic distances is less than 4% for B-D bond, and less than 3% for D-D bond), close to the calculated geometry. A quantitative agreement was found between experimental and calculated anisotropic temperature factors of individual atoms. For phonon energies $<15\text{ }\text{meV}$, the phonon density of states of ${\text{LiBH}}_{4}$ in the low-temperature phase depends quadratically on the phonon energy while for the high-temperature phase a linear dependence is observed, revealing a high lattice anharmonicity in the high-temperature phase. Moreover, an increased phonon density of states at low energies in the high-temperature phase compared to the low-temperature phase give a direct evidence for disorder in the high-temperature phase of ${\text{LiBH}}_{4}$ of the hydrogen sublattice which can originate from orientational disorder of ${\text{BH}}_{4}$ units. Potential energy landscape for rotation of ${\text{BH}}_{4}$ indicates that fairly localized minima and barriers higher than 0.6 eV exist in the low-temperature phase, i.e., ordered ${\text{BH}}_{4}$ ions. The high-temperature structure shows shallow barriers of $\ensuremath{\sim}0.2\text{ }\text{eV}$ without distinct energy minima, i.e., orientation of a single ${\text{BH}}_{4}$ unit cannot be precisely defined. This corroborates the large thermal displacements observed in diffraction studies and high disorder of ${\text{BH}}_{4}$ ions deduced from experimental partial phonon density of states in the high-temperature phase.

Finite-temperature lineshapes in gapped quantum spin chains

We consider the finite-temperature dynamical susceptibility $\ensuremath{\chi}(\ensuremath{\omega},q,T)$ of gapped quantum spin chains such as the integer spin Heisenberg and transverse field Ising models. At zero temperature $\ensuremath{\chi}$ in these models is dominated by a delta-function line arising from the coherent propagation of single-particle modes. Using methods of integrable quantum field theory, we determine the evolution of the lineshape at low temperatures. We show that the lineshape is in general asymmetric in energy. We discuss the application of our results to inelastic neutron-scattering experiments on gapped spin chain systems such as ${\text{Y}}_{2}{\text{BaNiO}}_{5}$ and ${\text{CsNiCl}}_{3}$.

Hydration Affects Both Harmonic and Anharmonic Nature of Protein Dynamics

To understand the effect of hydration on protein dynamics, inelastic neutron-scattering experiments were performed on staphylococcal nuclease samples at differing hydration levels: dehydrated, partially hydrated, and hydrated. At cryogenic temperatures, hydration affected the collective motions with energies lower than 5meV, whereas the high-energy localized motions were independent of hydration. The prominent change was a shift of boson peak toward higher energy by hydration, suggesting a hardening of harmonic potential at local minima on the energy landscape. The 240K transition was observed only for the hydrated protein. Significant quasielastic scattering at 300K was observed only for the hydrated sample, indicating that the origin of the transition is the motion activated by hydration water. The neutron-scattering profile of the partially hydrated sample was quite similar to that of the hydrated sample at 100K and 200K, whereas it was close to the dehydrated sample at 300K, indicating that partial hydration is sufficient to affect the harmonic nature of protein dynamics, and that there is a threshold hydration level to activate anharmonic motions. Thus, hydration water controls both harmonic and anharmonic protein dynamics by differing means.

Ｊ‐ＰＡＲＣで迎える結晶学の新展開 ２．Ｊ‐ＰＡＲＣがもたらす結晶学の新展開 非弾性散乱の生物への応用について

Ｊ‐ＰＡＲＣで迎える結晶学の新展開 ２．Ｊ‐ＰＡＲＣがもたらす結晶学の新展開 非弾性散乱の生物への応用について

Neutron-Scattering Study of the Localized Mode in β-Pyrochlore Superconductors AOs2O6

Inelastic neutron-scattering and neutron powder-diffraction experiments were carried out to investigate the localized mode, proposed from various bulk measurements, in the β-pyrochlore AOs 2 O 6 (A=K, Rb, Cs). The localized mode was identified in all three compounds as well as in another β-pyrochlore CsW 2 O 6 . The anharmonicity of the mode is weak in RbOs 2 O 6 and CsOs 2 O 6 but substantial in KOs 2 O 6 .

Two dimensionality of magnetic excitations on the trellis lattice:(La,Sr,Ca)14Cu24O41andSrCu2O3

We explore the properties of magnetic excitations on the trellis lattice which is relevant for the so-called telephone-number compounds ${A}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ with $A=(\mathrm{La},\mathrm{Sr},\mathrm{Ca})$ and the system $\mathrm{Sr}{\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$. The trellis lattice consists of two-leg ladders which are coupled in a strongly frustrated fashion. We use the effective model obtained for a single two-leg spin ladder to calculate the two-dimensional one-triplon dispersion and the corresponding one-triplon contribution to the dynamical structure factor. Special attention is laid on signatures of the frustrating interladder magnetic exchange. A detailed suggestion is made for an experimental detection of this exchange in inelastic neutron-scattering experiments.

Fermi liquid instabilities in the spin channel

We study the Fermi-surface instabilities of the Pomeranchuk type [Sov. Phys. JETP 8, 361 (1959)] in the spin-triplet channel with high orbital partial waves $[{F}_{l}^{a}(l>0)]$. The ordered phases are classified into two classes, dubbed the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases by analogy to the superfluid $^{3}\mathrm{He}$ A and B phases. The Fermi surfaces in the $\ensuremath{\alpha}$ phases exhibit spontaneous anisotropic distortions, while those in the $\ensuremath{\beta}$ phases remain circular or spherical with topologically nontrivial spin configurations in momentum space. In the $\ensuremath{\alpha}$ phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have a nearly isotropic underdamped dispersion relation at small propagating wave vectors. Due to the coupling to the Goldstone modes, the spin-wave spectrum develops resonance peaks in both the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ phases, which can be detected in inelastic neutron-scattering experiments. In the $p$-wave channel $\ensuremath{\beta}$ phase, a chiral ground-state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.

Lattice dynamics and thermodynamics of light actinides

In this paper, we present an ab initio study of the lattice dynamics of two light actinides, namely thorium and uranium. We worked within the framework of the quasi-harmonic approximation and by using density-functional theory, pseudo-potential method and linear response theory. We compare the phonon spectrums we obtained with inelastic neutron-scattering experiments.

Magnetic fluctuations at the field-tuned vs. concentration-tuned quantum phase transition in [formula omitted

CeCu 6 - x Au x has become a model system to study magnetic quantum phase transitions (QPT). In this system, the QPT can be tuned by Au concentration x , pressure, or magnetic field. Previous inelastic neutron-scattering (INS) experiments have demonstrated an anomalous scaling of the dynamical susceptibility at the concentration-tuned (zero-field) QPT for x = 0.1 , i.e., χ - 1 ( q , E , T ) = c - 1 [ θ α ( q ) + ( T - i E ) α ] , where θ ( q ) is a generalized Curie–Weiss temperature. This scaling suggests local criticality, with an anomalous exponent α ≈ 0.75 . Here we report on an INS study at the field-induced magnetic QPT of CeCu 5.8 Au 0.2 where the Néel temperature is driven to zero at a critical field of B ≈ 0.4 T , supplemented by specific-heat data. The INS data can be described better by the spin-density-wave scenario, i.e., χ - 1 ( Q AF , E , T ) = a - 1 ( T 3 / 2 - i bE ) where Q AF is the antiferromagnetic ordering wave vector, than by a local quantum critical point. This constitutes direct microscopic evidence for a difference in quantum fluctuation spectra at a magnetic QPT driven by different tuning parameters.

Spin dynamics of [formula omitted]=1 bond-alternating spin chains in transverse fields

We calculate dynamical structure factors of the S=1 bond-alternating spin chain in transverse magnetic fields. The numerical results successfully explain the field dependence of the peaks observed in recent inelastic neutron-scattering experiments on NTENP.

Effect of interchain coupling on spin correlation functions of spin-1 Heisenberg antiferromagnet CsNiCl3

The inelastic neutron-scattering experiment on CsNiCl 3 gives much bigger total intensity of multi-particle continuum than the theoretical calculation by the ( 1 + 1 )-dimensional O(3) non-linear σ -model. Three-dimensional effect has to be considered. A scenario was proposed where the interchain interaction is treated as an effective staggered magnetic field. We propose another model to approximately include the effect of the interchain coupling, and use the large- N expansion to do the calculations. In this circumstance we find that the Néel temperature is about 5 K, and also that for a range of wave-vectors the single magnon is unstable and will decay into three magnons.

Multiple scattering and attenuation corrections in Deep Inelastic Neutron Scattering experiments

Multiple scattering and attenuation corrections in Deep Inelastic Neutron Scattering experiments are analyzed. The theoretical basis of the method is stated, and a Monte Carlo procedure to perform the calculation is presented. The results are compared with experimental data. The importance of the accuracy in the description of the experimental parameters is tested, and the implications of the present results on the data analysis procedures is examined.

Spectroscopic, Magnetochemical, and Crystallographic Study of Cesium Iron Phosphate Hexahydrate: Characterization of the Electronic Structure of the Iron(II) Hexa-aqua Cation in a Quasicubic Environment

Spectroscopic, magnetochemical, and crystallographic data are presented for CsFe(H2O)6PO4, a member of a little-known isomorphous series of salts that facilitates the study of hexa-aqua ions in a quasicubic environment. Above 120 K, the deviations from cubic symmetry are minimal, as shown by the first example of an iron(II) Mössbauer spectrum that exhibits no measurable quadrupole splitting. Two crystallographically distinct [Fe(OH2)6]2+ complexes are identified from inelastic neutron-scattering (INS) experiments conducted between 2 and 15 K. The data are modeled with the ligand-field Hamiltonian, H = lambdaLŝ + betaB(kL + 2ŝ) + Delta(tet){Lz2 - (1/3)L(L + 1)} + Delta(rhom){Lx2 - Ly2}, operating in the ground-term (5)T(2g) (Oh) basis. An excellent reproduction of INS, Mössbauer, HF-EPR, and magnetochemical data are obtained in the 2 and 15 K temperature regimes with the following parameters: lambda = -80 cm(-1); k = 0.8; site A Delta(tet) = 183 cm(-1), Delta(rhom)= 19 cm(-1); site B Delta(tet) = 181 cm(-1), Delta(rhom)= 12 cm(-1). The corresponding zero-field-splitting (ZFS) parameters of the conventional S = 2 spin Hamiltonian are as follows: site A D = 12.02 cm(-)(1), E = 2.123 cm(-1); site B D = 12.15 cm(-1), E = 1.37 cm(-1). A theoretical analysis of the variation of the energies of the low-lying states with respect to displacements along selected normal coordinates of the [Fe(OH2)6]2+, shows the zero-field splitting to be extremely sensitive to small structural perturbations of the complex. The expressions derived are discussed in the context of spin-Hamiltonian parameters reported for the [Fe(OH2)6]2+ cation in different crystalline environments.

Multiple magnetic singlet-singlet excitations in intermetallic PrNiSn

Inelastic neutron-scattering experiments have been carried out on a polycrystalline sample of PrNiSn, and seven of the eight excited crystal-field singlets of the Pr ions were detected. The system stays paramagnetic, at least down to $0.9\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the three principal susceptibility components have been measured on a PrNiSn single crystal between room temperature and $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The crystal-field excitations of the single crystal at low temperatures have been studied by triple-axis neutron spectroscopy. Dispersive effects are observed for three different levels of singlet-singlet excitations. The results are analyzed in terms of a mean-field/random phase approximation model, and it is concluded that the exchange interaction is highly anisotropic and of long range. The critical ratio between the maximum of the exchange interaction and that required for inducing a magnetic ordering of the singlet ground-state system is derived to be 0.48, leading to a predicted ordering temperature of $6\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ for the combined electron-nuclear magnetic system.

Gen Shirane

Gen Shirane

Development of the very low angle detector for epithermal neutron scattering at low momentum transfers

The design and prototype tests of the Very Low Angle Detector (VLAD) for epithermal neutron scattering at low momentum transfers are presented. The detector will be installed on the VESUVIO spectrometer at the ISIS spallation neutron source for so-called High-energy Inelastic Neutron Scattering (HINS) experiments. It will consist of an array of Resonant Detectors (RD) covering the scattering range 1/spl deg/-5/spl deg/. The results of prototype tests with a reduced set of RD units demonstrate the feasibility of the measurement in the adverse environmental conditions of ISIS. Simulations of particle interactions using the GEANT4 code show that the envisaged detector design can meet the requirements in terms of efficiency, cross-talk between detection channels and neutron scattering events in the detector.

Resolution of the VESUVIO spectrometer for High-energy Inelastic Neutron Scattering experiments

New perspectives for epithermal neutron spectroscopy have been opened up as a result of the development of the Resonance Detector and its use on inverse geometry time-of-flight spectrometers at spallation sources. A special application of the Resonance Detector is the Very Low Angle Detector Bank (VLAD) for the VESUVIO spectrometer at ISIS, operating in the angular range 1 ∘ < 2 θ < 5 ∘ . This equipment allows High-energy Inelastic Neutron Scattering (HINS) measurements to be performed in the ( q , ω ) kinematical region at low wavevector ( q < 10 Å - 1 ) and high energy (unlimited) transfer ℏ ω > 500 meV , a regime so far inaccessible to experimental studies on condensed matter systems. The HINS measurements complement the Deep Inelastic Neutron Scattering (DINS) measurements performed on VESUVIO in the high wavevector q ( 20 Å - 1 < q < 250 Å - 1 ) and high energy transfer ( ℏ ω > 1 eV ) , where the short-time single-particle dynamics can be sampled. This paper will revise the main components of the resolution for HINS measurements of VESUVIO. Instrument performances and examples of applications for neutron scattering processes at high energy and at low wavevector transfer are discussed.

Dynamical properties ofS=1bond-alternating Heisenberg chains in transverse magnetic fields

We calculate dynamical structure factors of the S=1 bond-alternating Heisenberg chain with a single-ion anisotropy in transverse magnetic fields, using a continued fraction method based on the Lanczos algorithm. In the Haldane-gap phase and the dimer phase, dynamical structure factors show characteristic field dependence. Possible interpretations are discussed. The numerical results are in qualitative agreement with recent results for inelastic neutron-scattering experiments on the S=1 bond-alternating Heisenberg-chain compound $\rm{Ni(C_{9}D_{24}N_{4})(NO_{2})ClO_{4}}$ and the S=1 Haldane-gap compound $\rm{Ni(C_{5}D_{14}N_{2})_{2}N_{3}(PF_{6})}$ in transverse magnetic fields.

Absence of an isotope effect in the magnetic resonance in high-Tcsuperconductors

An inelastic neutron scattering experiment has been performed in the high-temperature superconductor $\rm YBa_2Cu_3O_{6.89}$ to search for an oxygen-isotope shift of the well-known magnetic resonance mode at 41 meV. Contrary to a recent prediction (I. Eremin, {\it et al.}, Phys. Rev. B {\bf 69}, 094517 (2004)), a negligible shift (at best $\leq$ +0.2 meV) of the resonance energy is observed upon oxygen isotope substitution ($^{16}$O$\to^{18}$O). This suggests a negligible spin-phonon interaction in the high-$T_c$ cuprates at optimal doping.