Self-induced resonant optical rotation in crystals KCl:Li

The specific rotation of the resonant radiation polarization plane predicted earlier for cubic crystals with tunneling centers is observed in KCl containing F_A(Li) centers. The rotation is supposed to be connected essentially with the well-known off-center position of Li⁺ ion. The simple theory based on this assumption agrees with the experimental data.     

An origin of infinite range dipole-dipole correlations in soft matrices with off-center impurities: K 1−x Li x Ta 1−y Nb y O 3 and other systems

A model of cooperative behaviour for K 1 m x Li x Ta 1 m y Nb y O 3 (KLTN) and for other disordered systems like ferroelectric relaxors is considered from the point of view of contribution of infinite-range dipole-dipole interactions. It is shown that a local piezoeffect for off-center impurities in crystals with rather high electrostriction is responsible as origin of a infinite-range electric dipole-dipole interaction via elastic fields as well as for a co-existence of ferroelectric and glass-like states with reentrant glass effect.     

Editorial

This review contains up-to-date information about experimental and theoretical investigations of phase transitions and specific features of properties of mixed crystals involving the incipient ferroelectric KTaO₃ with the off-center Li⁺, Nb⁵⁺, Na⁺ impurities. Main attention is paid to the results of the study of the mixed systems by radiospectroscopy methods (ESR and NMR).

Theoretical criteria and experimental evidence of ferroelectric and ferroelastic phase transitions as well as of dipole and quadrupolar glass states induced by the off-center impurities are discussed. It is shown that at high enough concentrations of the off-center impurities phases with long-range order appear, but at low concentrations dipole glass states occur. At intermediate concentrations of the off-center impurities new phases appear in which the coexistence of long-range properties and those of dipole glasses is possible. These phases could be named ferroelectric or ferroelastic glasses to stress their similarity with the ferroglass phases which were discovered earlier in mixed magnetic systems. The usefulness of radiospectroscopy methods for the study of phase transitions induced by off-center impurities in mixed systems, which can be considered as model disordered systems, is underlined.

In conclusion, some questions on the physics of phase transitions in disordered systems which should be solved in the future are discussed.     

Electronic states of CsLi and CsLi<Superscript>+</Superscript> molecules

Configuration interaction calculations have been carried out on electronic states of the CsLi molecule and the CsLi⁺ cation. Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels are presented for the lowest states of ^1,3Σ⁺, ^1,3Π, and ^1,3Δ symmetries of the alkali dimer CsLi molecule dissociating into Cs (6s, 6p, 5d, 7s, and 7p) + Li (2s, 2p, 3s, 3p, and 3d) as well as for the lowest ²Σ⁺, ²Π, and ²Δ electronic states of the CsLi⁺ cation dissociating into Li (2s, 2p, 3s, 3p, and 3d) + Cs⁺ and Li⁺ + Cs (6s, 6p, 5d, 7s, and 7p). The results of the present many-electron configuration interaction calculations on the cation support the previous core-polarization effective potential calculations. The present calculations on the CsLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. We have used an ab initio approach involving a nonempirical pseudopotential for the Li (1s²) and Cs cores and a core-valence correlation correction. A very good agreement of data from spectroscopic constants for some of the lowest states of the CsLi and CsLi⁺ molecules with those available in recent theoretical works has been obtained. The existence of numerous avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries is related to a charge transfer process between the two ionic CsLi⁺ and LiCs⁺ systems.     

Diffractive scattering of loosely bound nuclei involving two charged clusters on nuclei

The theory of diffractive interaction between loosely bound nuclei featuring two charged clusters and nuclei is developed with allowance for Coulomb interaction. The differential cross sections for the scattering of ⁶Li, ⁷Be, and ⁸B nuclei on ¹²C nuclei are calculated, and the results of these calculations are compared with data from recent experiments.     

Off-center Li defects in KCl: Parameters for isolated Li+ as a function of hydrostatic pressure and evidence for other Li centers

Abstract

We have measured all three tunneling parameters for the KCl:Li system as a function of hydrostatic pressure; all increase with pressure. Our measurements show that the off-center tunneling model works exceedingly well for this system. Surprisingly, the pressure dependence of the electric dipole moment shows a sharp break near 900 bar. In some samples, additional lines indicate other Li centers are present, possibly Li pairs.     

Structure of light neutron-rich nuclei and mechanism of elastic proton scattering

Differential cross sections for elastic p ⁶He, p ⁸Li, and p ⁹Li scattering at two energies of 70 and 700 MeV per nucleon were calculated within the Glauber theory of multiple diffractive scattering. Threeparticle wave functions (α-n-n for ⁶He, α-t-n for ⁸Li, and ⁷Li-n-n for ⁹Li) were used for realistic potentials of intercluster interactions. The sensitivity of elastic scattering to proton-nucleus interaction and to the structure of nuclei was explored. In particular, the dependence of the differential cross section on the contribution of higher order collisions, on scattering on the core and peripheral nucleons, and on the contribution of small wave-function components and their asymptotic behavior was determined. A comparison with available experimental data and with the results of calculations within different formalisms was performed.     

Influence of the atomic polarization potential on the tunneling rates of electrons between atoms and surfaces

The tunneling rate of electrons between a Li⁻ ion and a surface is studied using the coupled angular mode method and the complex scaling method. The comparison of the two sets of results obtained with various representations of the e⁻Li interaction and their analysis shows that the e⁻Li polarization potential plays an important role in determining the tunneling rates. This effect is attributed to a lowering of the potential barrier between the atom and the surface.     

Study of short-lived silver isotopes with a laser ion source

The continuum part of the⁶Li (a,a)⁶Li (1.47–2.47 MeV) scattering data at E_a=50 MeV are extracted in two discretized bins. Coupled-channel calculations are carried out coupling the 1⁺ ground state of⁶Li with both the resonant, 3⁺ ₁ state, and two non-resonant continuum states. The discretized continuum of the⁶Li (p,p)⁶Li (1.75–3.25 MeV) scattering data at E_p=65 MeV are also analysed on the same footing. In both the cases the effect of coupling is found to be minimal.     

Fermion-mediated long-range interactions between bosons stored in an optical lattice

We describe a new method for creating spin-dependent long-range interactions between atomic ultra-cold neutral bosons—specifically ⁸⁷Rb—in an optical lattice. In this proposal, the bosonic system is immersed in a spin-polarized degenerate Fermi gas (almost perfectly non-interacting), here ⁶Li. We first show that the bosons acquire a long-range interaction analogous to Ruderman–Kittel–Kasuya–Yosida interaction in solids. The resulting fermion-mediated Bose–Bose interaction, which can depend on the bosons’ spin state, is tunable using inter-species Feshbach resonance. When the bosons are subject to a suitable optical lattice, 3-body loss processes are greatly suppressed. We conclude by showing that these interactions can lead to a supersolid phase for single-spin Bose system, and also to a fully tunable transverse field Ising model for a two-component Bose system.     

Comparative analysis of the characteristics of the elastic scattering of protons by lithium isotopes 6, 7, 8, 9Li, performed using Glauber’s multiple diffraction scattering theory

Differential cross sections and vector analyzing powers are calculated for the elastic scattering of protons by lithium isotopes ⁶Li, ⁷Li, ⁸Li, and ⁹Li at energies of 60 and 200 MeV. The calculations are performed using Glauber??s multiple diffraction scattering theory in the two-particle (for ⁷Li) and three-particle (for ^6,8,9Li) models with realistic intercluster interaction potentials. An analysis of the relationship between the differential elastic scattering cross section and various wave functions, calculated using different interaction potentials, is presented for the ^{8, 9}Li isotopes.     

Polarization in the quasielastic scattering of 1-GeV/c protons on light nuclei

Polarization measurements in the A(p, 2p)B reactions on ⁶Li, ⁷Li, and ²⁸Si nuclei at a proton-beam energy of 1 GeV were performed in a kinematically complete experiment. By using a two-arm magnetic spectrometer, two secondary protons were recorded in coincidence at asymmetric scattering angles of θ₁=15°?26° and θ₂=58.6° for residual-nucleus momenta in the range K _B=0–150 MeV/c. Either arm of the spectrometer was equipped with polarimeters based on proportional chambers. The data coming from this experiment are analyzed within the distorted-wave impulse approximation. It is shown that the polarization of recoil protons formed at angle θ₂ in the interaction featuring a proton from the P shell of the ⁷Li nucleus can be described under the assumption of an effective intranuclear-proton polarization by using the single-particle shell-model wave function of the nucleus. Our data on the polarizations of the two protons from the reaction (p, 2p) on a ²⁸Si nucleus also suggest the effective polarization of the protons in the D shell of the ²⁸Si nucleus. It is found that, for high recoil-nucleus momenta of K _B≥90 MeV/c, the effective polarization of the protons in the P shell of the ⁶Li nucleus—this polarization was discovered in studying the polarization of recoil protons in the reaction ⁶Li(p, 2p)⁵He—cannot be described within the shell model assuming LS coupling. As might have been expected, the polarization of recoil protons knocked out from the S shells of the ⁶Li and ⁷Li nuclei comply well with the predictions obtained in the impulse approximation with allowance for the depolarization effect alone.     

Strong reaction channels at barrier energies in the system 6Li + 208Pb

Large cross-section reaction channels were measured in the systems ⁶Li( ⁷Li) + ²⁰⁸Pb with high statistical accuracy at 5(3) energies around the Coulomb barrier from 29 to 39 MeV. These channels were assigned (mainly) to the breakup of ⁶Li, very loosely bound, into α + d and to the breakup of ⁵Li, produced by n-transfer to the target, into α + p and to similar processes with ⁷Li beam. The cross-sections with ⁶Li, S _α = 1.475 MeV, are systematically larger than the ⁷Li ones. This reflects, most likely, the higher binding energy of ⁷Li, S _α = 2.468 MeV. Theoretical predictions for the ⁶Li + ²⁰⁸Pb system which include for ⁶Li breakup to continuum states within a continuum discretized coupled-channels approach (CDCC) and resonant breakup plus n-transfer with DWBA reproduce the angular distribution shapes but still underestimate the cross-sections by a factor ∼ 3. Received: 15 January 2001 / Accepted: 3 March 2001     

Orientationally degenerate (OH)− centers in perovskite-type proton-conducting oxides: Low-temperature thermodynamics and H/D isotope effects

It is shown that proton-associated dipole centers (OH)⁻ can provide significant, glasslike contributions to the low-temperature properties of perovskite-type proton conducting oxides, such as ABO_3−y , doped with cations of lower valence. These contributions result from the splitting of the orientationally degenerate states of dipole centers by random crystal fields and proton tunneling. It is demonstrated that H/D (or H/T) substitution leads to large and abnormal isotope effects for the properties caused by (OH)⁻ degenerate states. The text was submitted by the authors in English.     

Scattering and transfer reactions for 6, 7Li + 90, 91Zr

Elastic scattering data have been measured for the ⁷Li + ⁹⁰Zr, ⁶Li + ⁹⁰Zr, and ⁶Li + ⁹¹Zr systems at E(Li) = 34 MeV. Inelastic scattering data for the ⁷Li + ⁹⁰Zr and ⁶Li + ⁹⁰Zr systems were also measured for the 2⁺(2.18 MeV) and 3^?(2.75 MeV) states in ⁹⁰Zr and the $\text{1}\text{2}{}^{\mathrm{?}}\text{(0.48}\text{MeV}\text{)}$ state in ⁷Li. Optical model analyses of the elastic scattering data and DWBA analyses for the states in ⁹⁰Zr were performed. The deduced deformation lengths for the 2⁺ state agreed with those extracted in other studies but the deformation length for the 3^? state was smaller. The ⁹⁰Zr(⁷Li, ⁶Li)⁹¹Zr angular distributions were measured for the 1.21 and 2.03 MeV states and the 2.19 MeV doublet in ⁹¹Zr. Also, ⁹⁰Zr(⁷Li, ⁶He)⁹¹Nb angular distributions were measured for the ground states, 0.10, 3.41 and 4.82 MeV states in ⁹¹Nb. The transitions well matched in angular momentum were described by finite-range DWBA calculations, while other transitions displayed the same phase problems seen with heavier ions. The extracted spectroscopic information was consistent with the results of other reaction studies. At the present energy, it was not possible to determine whether the l = 1 phase problem that occurs for heavy-ion single-nucleon transfer reactions on 2s-1d shell nuclei occurs in ⁹¹Zr also.     

Astrophysical <Emphasis Type="Italic">S</Emphasis> factor for the radiative-capture reaction <Emphasis Type="Italic">p</Emphasis><Superscript>6</Superscript>Li → <Superscript>7</Superscript>Beγ

A new measurement of differential cross sections for elastic p ⁶Li scattering in the energy range 0.35–1.2 MeV was performed. A partial-wave analysis of the data obtained in this way was carried out, and potentials simulating the p ⁶Li interaction were constructed. Various experiments devoted to studying elastic p ⁶Li scattering over the broad energy range of 0.5–50 MeV were analyzed on the basis of the optical model. By using the potentials obtained from the partial-wave analysis, the possibility of describing the astrophysical S factor for radiative proton capture on ⁶Li at low energies was considered within the potential cluster model involving forbidden states.     

锂里德堡态的d-f间隔的共振计算

应用全实加关联方法计算而得到的锂原子的1s2nd (n=3–5) 态 和 1s2nf (n=4–6) 态的能量，我们可以通过量子亏损理论得到量子亏损函数，它随着能量平缓地变化。利用这些函数可以分别构造一个系统方程去求解锂原子1s2nd和 1s2nf (n=7–11)里德堡态的能量和量子亏损。我们计算了nd和nf 中心能级 (n=7–11)的间隔并和文献中已有的实验和理论数据做了比较。     

Proton momentum distributions in the 7Li nucleus in a potential cluster model

Distributions of the proton momentum in the ⁷Li{αt} → p + ⁶He{αnp} fragmentation channel were, along with the corresponding widths and spectroscopic factors, calculated in the αnn model representation of wave functions of the ⁶He nucleus in the (0⁺,1) ground and (2⁺,1) excited states. The results are compared to the available theoretical calculations and experimental NIKHEF data on the ⁷Li(e,e′p)⁶He electron-induced proton knock-out process.     

The 7Li (n,γ)8Li radiative capture at astrophysical energies

The possibility to construct intercluster interaction potentials in continuous and discrete spectra is shown in one‐channel cluster model based on the classification of orbital states according to Young schemes. These potentials usually contain Pauli forbidden states, and correctly describe elastic scattering phase shifts taking into account resonance behavior and main characteristics of the bound states of nuclei in the considering cluster channel. The versions of intercluster interaction potentials describing the resonance nature of some phase shifts of the n⁷Li elastic scattering at low energies and the P₂ ground state of ⁸Li in the n⁷Li cluster channel have been constructed for the demonstration of this approach. The possibility of describing the total cross sections of ⁷Li (n,γ)⁸Li within the energies from 5 meV (5 · 10^‐3 eV) to 1 MeV, including resonance at 0.25 MeV, has been demonstrated for the potentials obtained in the potential cluster model with forbidden states.     

Interaction of α particles with 6Li and 7Li nuclei at low energies

The reaction of radiation capture (α, γ) on ⁷Li and ⁶Li nuclei, which is of importance in dt-plasma diagnostics, was studied. It was shown that the cross-section resonant structure of the (α, γ) reaction on ⁷Li and ⁶Li nuclei is determined by the structural features of the excited states of ¹¹B and ¹⁰B nuclei, which have narrow α widths.