Inelastic x-ray scattering in correlated Mott insulators

We calculate the inelastic light scattering from x rays, which allows the photon to transfer both energy and momentum to the strongly correlated charge excitations. We find that the charge-transfer peak and the low-energy peak both broaden and disperse through the Brillouin zone similar to what is seen in experiments in materials such as Ca2CuO2Cl2.     

小角x射线散射结晶聚合物结构的研究

利用结晶聚合物的“三相结构”模型计算了结晶聚合物的一维电子密度相关函数,结论是三相模型的片层厚度和不变量与两相结构的意义不同.利用计算结果分析了一批样品的结构参量,发现用Ruland方法得到的结晶过渡层的厚度与用一维电子密度相关函数的结果是一致的.用Bragg定律求出的结晶聚合物的长周期与相关函数法长周期相差很多.这是因为两种分析结晶过渡层厚度的方法都是以样品电子密度的不均匀区为基础的,本质是一致的.但是Bragg法的长周期与相关函数法的长周期代表的范围不同 关键词： 小角x射线散射 结晶聚合物 三相结构 相关函数     

Inelastic neutron scattering study of antiferromagnetic CoO

In order to study the energy levels of the magnetic excitations in antiferromagnetic CoO, we have measured the cross-section for inelastic n-scattering of CoO powder at various scattering angles θ and energy transfer from 15 to 70 meV. For large θ purely nuclear scattering is observed, while for small θ the cross-section is predominantly due to magnetic scattering with some nuclear contributions. The cross-section shows several peaks, which have not yet been observed.By comparison of the results of pure CoO and of Co_0.8Ni_0.2O two peaks in the cross-section can be assigned to single ion-like transitions in the ground state multiplet of Co²⁺ in the antiferromagnetic phase. The parameters of a simple molecular field model are discussed.     

Inelastic neutron scattering study of spin waves in MnO

The dispersion relation E(q) for spin waves in MnO has been measured at 4.2°K by neutron inelastic scattering. The isotropic exchange integrals as well as the anisotropy constants have been determined by fitting the Hamiltonian to the data. It is found that the exchange striction plays main role in the anomaly in the magnetic interactions in MnO and the biquadratic exchange interaction j₁(S₁·S₂)² is almost absent (j₁/J₁ ? 0.002).     

Magnetooptical absorption of a molecular crystal in the exciton frequency range

Nonlinear absorption of a molecular crystal in an external magnetic field is considered. The exciton absorption shape functions under polarized laser radiation and a weak magnetic field, as well as the mechanisms responsible for the formation of a hysteresis loop in the dependence of the output light intensity on the applied magnetic field, were studied for the particular case of benzene. It was established that, for the magnetooptical response of the molecular crystal under study, the formation of bistable loops is inverse in character, which makes it possible to monitor and control the behavior of bistable elements in optical logics systems with an external magnetic field at a fixed illumination frequency.     

Superliquid state of an exciton mixture with small exciton radii in molecular crystals

The energy spectrum of excitons with a small radius in a superliquid state in molecular crystals has been investigated. A more complicated structure of the exciton energy spectrum with a number of equivalent minima for k 0 has been considered. The problem was solved as that of determining the energy spectrum of a mixture of various types of non-ideal exciton gases in a superliquid state, corresponding to the individual exciton energy minima. The appropriate branches of the energy spectrum of elementary excitations (hydrons) have been determined and the conditions for their stability have been investigated.     

Inelastic neutron scattering study of commensurate-incommensurate phase transition in thiourea

This paper presents a study of the nature of the incommensurate lattice instability in deuterated thiourea by inelastic neutron scattering. It shows clearly a “soft mode” which condenses at the phase transition in a satellite reflexion. A study of related dispersion curves along the [O ξ O] direction shows an unusual spectral shape in a large temperature range above T_c.     

Inelastic neutron scattering study of structural phase transitions in polyphenyls

Inelastic neutron scattering was used to study structural phase transitions in polyphenyls. These transitions result from the stabilization of the non-planar molecular configuration with respect to a torsional angle between the planes of phenyl rings. For biphenyl the zone boundary mode shows a pronounced softening in the temperature range 60–200 K and becomes overdamped close to the transition temperature. For p-terphenyl the spectrum contains a quasi-elastic anisotropic central component diverging on lowering the temperature.     

Weak exciton scattering in molecular nanotubes revealed by double-quantum two-dimensional electronic spectroscopy

The two-exciton manifold of a double-wall cylindrical molecular aggregate is studied using a coherent third order optical technique. Experiments reveal the anharmonic character of the exciton bands. Atomistic simulations of the exciton-exciton scattering show that the excitons can be treated as weakly coupled hard-core bosons. The weak coupling stems from the extended exciton delocalization made possible by the nanotube geometry.     

Inelastic electron scattering in nickel

Using a 200 keV electron spectrometer, with an energy resolution of ～0.25 eV and a momentum resolution of ～0.2 A^-1, we have measured the energy loss spectra for transmission of electrons through thin (～600 Å) Ni films. These results address the general question of the validity of momentum transfer estimates in electron loss scattering.Using low-energy electron backscattering, we have observed the dipole forbidden M₁ transition at 112 eV. For high-energy scattering, we have observed this transition only at high momentum transfer (q? 2 A^-1). These results indicates sizable contributions from high momentum transfer collisions in the low-energy experiments.     

Anisotropic nuclear inelastic scattering of an iron(II) molecular crystal

Nuclear inelastic scattering (NIS) spectra were recorded for a monocrystal of the spin-crossover complex [Fe(tptMetame)] (ClO (4))(2) (tptMetame = 1,1,1-tris([N-(2-pyridylmethyl)-N-methylamino]-methyl)ethane) at T = 30 K (low-spin state) and at room temperature (high-spin state) for different crystal orientations. The high energy resolution (0.65 meV) allowed us to resolve individual molecular vibrations which were unambiguously identified by density functional calculations. From the NIS spectra for the first time the angular-resolved iron-partial density of phonon states (PDOS) was extracted. The PDOS corroborates a vibrational entropy difference as driving force of the spin transition.     

Collective excitations in exciton crystal

Crystal phase of indirect excitons formed by spatially separated electrons and holes in coupled quantum wells is analyzed. The collective mode spectrum of the exciton crystal at zero and nonzero agnetic fields is found. The spectrum consists of two optical and two acoustical modes (transverse and longitudinal in each case). We also study changes of the dipole crystal collective excitations at the transition exciton crystal-electron-hole plasma.     

Inelastic scattering of an X-ray photon by a manganese atom

The influence of multiplet and many-particle effects on the shape and magnitude of the double differential cross section of resonant inelastic scattering of a linearly polarized X-ray photon by a free atom with an open shell in the ground state within the energy range of the K ionization threshold is theoretically investigated using a manganese atom as an example. The radial relaxation of electron shells, spin-orbit and multiplet splittings, configuration mixing in intermediate scattering states, and Auger and radiative decays of newly formed vacancies are taken into account. The results of the calculation are predictive.     

Inelastic neutron scattering study of acoustic phonons of black phosphorus

Dispersion relations of acoustic phonons of the orthorhombic black phosphorus have been measured at room temperature and atmospheric pressure. Very anisotropic dispersion surfaces were observed along the three principal directions. Comparison is made between the present measurements and the recent calculations of dispersion curves by Kaneta et al.