Single-particle dynamics of the solid heliums from deep inelastic neutron scattering

1987 ◽  
Vol 65 (11) ◽  
pp. 1401-1408 ◽  
Author(s):  
R. O. Simmons
Keyword(s):  
Neutron Scattering ◽  
Single Particle ◽  
Inelastic Neutron Scattering ◽  
Solid Helium ◽  
Dynamic Structure ◽  
Inelastic Neutron ◽  
Hexagonal Close Packed ◽  
Theoretical Predictions ◽  
Atomic Momentum ◽  
Particle Property

Previous neutron-scattering research on solid heliums has been restricted to small momentum transfers, Q, both by large Debye–Waller factors and by scientific interest being restricted to collective modes and their interactions. It has also been limited by insufficient sources of neutron beams of about an electronvolt in energy, which are required to apply the method of deep inelastic scattering to solids. Making use of a spallation neutron source and a suitable chopper spectrometer, one can now collect data in which the dynamic structure factor S(Q,E) directly reflects the atomic-momentum distribution n(p). For 4He, the major determining factor on this single-particle property is the density of the sample, not its microscopic structure. At a strictly constant number density, samples of hexagonal close-packed (hcp), body-centered cubic (bcc), and normal liquid show identical S(Q,E)'s for Q's near 200 nm−1, at current levels of precision. The case of bcc 4He is used to illustrate the method, and the derived kinetic energy is compared with theoretical predictions. The applicability of these results in other areas of solid-helium physics is indicated.

Deep Inelastic Neutron Scattering Studies of Atomic Momentum Distributions in Condensed Argon and Neon

1993 ◽  
Vol 48 (1-2) ◽  
pp. 438-442
Author(s):  
M. A. Fradkin ◽  
S.-X. Zeng ◽  
R. O. Simmons
Keyword(s):  
Neutron Scattering ◽  
Wave Vector ◽  
Inelastic Neutron Scattering ◽  
Dynamic Structure ◽  
Inelastic Neutron ◽  
Longitudinal Momentum ◽  
Final State ◽  
Momentum Distribution Function ◽  
Atomic Momentum ◽  
Liquid Neon

Abstract Using deep inelastic neutron scattering, direct measurements have been made, i) of the dynamic structure factor of a series of condensed argon samples over the temperature range 18 to 85 K, near melting (for wave-vector transfers 12 to 26 Ä -1) and ii) of liquid neon, near 27 K (for wave-vector transfers 10.4 to 27.6 Ä -1). Neutron time-of-flight chopper spectrometers were employed. Single-particle kinetic energies, £ k , can be obtained from the analysis of the Doppler-broadened recoil spectrum of the target particles. For argon the temperature dependence of £ k can be compared to expectations from theory, from thermodynamic data, and from previous neutron scattering measurements on collective vibrational modes. For liquid neon the wave-vector-transfer dependence of J{y), the longitudinal momentum distribution function, is being analyzed for final-state effects.

QUANTIZED INTRINSICALLY LOCALIZED MODES: LOCALIZATION THROUGH INTERACTION

2012 ◽  
Vol 11 ◽  
pp. 12-21
Author(s):  
PETER S. RISEBOROUGH
Keyword(s):  
Neutron Scattering ◽  
Experimental Observation ◽  
Phonon Spectrum ◽  
Bound States ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Localized Modes ◽  
Scattering Spectrum ◽  
Theoretical Predictions ◽  
Quartic Anharmonicity

We have calculated the lowest energy quantized spectra of Intrinsically Localized Modes (ILMs) for the Fermi-Pasta-Ulam lattices. The quantized ILM spectra are composed of resonances in the two-phonon continuum and branches of infinitely long-lived excitations that are bound states formed from even numbers of phonons. For quartic anharmonicity and one atom per unit cell, the calculated ILMs are consistent with the results of previous calculations using the number conserving approximation. However, by contrast the ILM spectrum of the lattice with cubic interactions couples resonantly with the single-phonon spectrum and cannot be calculated within a number conserving approximation. Furthermore we argue that, by introducing a sufficiently strong cubic non-linearity, the quantized ILMs can be observed directly through the single-phonon inelastic neutron scattering spectrum. We compare our theoretical predictions with the recent experimental observation of breathers in NaI by Manley et al.

scholarly journals Suppressed-moment 2-k order in the canonical frustrated antiferromagnet Gd2Ti2O7

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Joseph A. M. Paddison ◽  
Georg Ehlers ◽  
Andrew B. Cairns ◽  
Jason S. Gardner ◽  
Oleg A. Petrenko ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Spin Wave ◽  
Inelastic Neutron Scattering ◽  
Magnetic Moments ◽  
Magnetic Ordering ◽  
Thermal Fluctuation ◽  
Inelastic Neutron ◽  
Scattering Measurements ◽  
Theoretical Predictions ◽  
Powder Samples

AbstractIn partially ordered magnets, order and disorder coexist in the same magnetic phase, distinct from both spin liquids and spin solids. Here, we determine the nature of partial magnetic ordering in the canonical frustrated antiferromagnet Gd2Ti2O7, in which Gd3+ spins occupy a pyrochlore lattice. Using single-crystal neutron-diffraction measurements in applied magnetic field, magnetic symmetry analysis, inelastic neutron-scattering measurements, and spin-wave modeling, we show that its low-temperature magnetic structure involves two propagation vectors (2-k structure) with suppressed ordered magnetic moments and enhanced spin-wave fluctuations. Our experimental results are consistent with theoretical predictions of thermal fluctuation-driven order in Gd2Ti2O7, and reveal that inelastic neutron-scattering measurements on powder samples can solve the longstanding problem of distinguishing single-k and multi-k magnetic structures.

Crystal field effects on the inelastic neutron scattering from heavy rare earth metals in the paramagnetic phase

1968 ◽  
Vol 46 (12) ◽  
pp. 1499-1501 ◽  
Author(s):  
A. D. B. Woods
Keyword(s):  
Rare Earth ◽  
Neutron Scattering ◽  
Crystal Field ◽  
Inelastic Neutron Scattering ◽  
Order Term ◽  
Rare Earth Metals ◽  
Inelastic Neutron ◽  
Paramagnetic Phase ◽  
Heavy Rare Earth ◽  
Hexagonal Close Packed

Expressions which arise in the interpretation of inelastic neutron scattering from hexagonal close packed rare earth metals in the paramagnetic phase are presented and discussed. It is concluded that the fourth- and sixth-order terms which occur in the Hamiltonian describing the crystal field can, in some cases, be as important as the leading second-order term.

Magnetic Specific Heat of Cd1−xMnxTe at Low Temperatures and High Magnetic Fields

1986 ◽  
Vol 89 ◽  
Author(s):  
W. Y. Ching ◽  
D. L. Huber
Keyword(s):  
Specific Heat ◽  
Low Temperatures ◽  
Inelastic Neutron Scattering ◽  
Exchange Interactions ◽  
Dynamic Structure ◽  
Inelastic Neutron ◽  
Magnetic Specific Heat ◽  
Theoretical Predictions ◽  
Use Values ◽  
Applied Fields

AbstractTheoretical predictions for the magnetic specific heat of Cd1−xMnxTe:x=0.20, 0.35, 0.50, and 0.65 are reported for B=0, 10T, and 100T. The analysis applies to the low-temperature regime, T≤10K, where the fundamental excitations are harmonic magnons. The calculations use values for the exchange interactions which were inferred from fits to the dynamic structure factor describing inelastic neutron scattering at low temperatures. For x=0.35, 0.50, and 0.65 the specific heat is only weakly affected by applied fields up to 10T. At the lowest concentration the application of a field of 10T leads to a significant reduction in the specific heat. Results are also presented for the distribution of magnon modes at various concentrations and fields.

MAGNETIC EXCITATION OF ORTHOGONAL DIMER HEISENBERG SPIN SYSTEM FOR SrCu2(BO3)2

2003 ◽  
Vol 17 (28) ◽  
pp. 5047-5051
Author(s):  
S. MIYAHARA ◽  
K. TOTSUKA ◽  
K. UEDA
Keyword(s):  
Neutron Scattering ◽  
Bound States ◽  
Inelastic Neutron Scattering ◽  
Perturbation Technique ◽  
Dynamic Structure ◽  
Inelastic Neutron ◽  
Magnetic Behaviour ◽  
Lanczos Method ◽  
Flat Band ◽  
Two Dimensional

SrCu 2( BO 3)2 is a new two-dimensional spin gap system and the magnetic behaviour of this compound is explained well by the two-dimensional orthogonal dimer Heisenberg model. Recently several excitations have been observed by inelastic neutron scattering and other experiments. We study features of these excitations by Lanczos method and perturbation technique. A triplet excitation has an almost localised nature. This localised character is observed as an almost flat band in neutron scattering. On the other hand, bound states of two triplet excitations, which have dispersive character, are stable in contrast to ordinary magnetic systems. We calculate the dynamic structure factor by a Lanczos method in finite systems and compare our results with experiments.

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