Jahn-Teller effect on Sm3+ ions in fluctuating-valence compounds

The dynamic and static Jahn-Teller effects are observed in ESR on rare-earth ions, specifically, on Sm³⁺ ions in the fluctuating-valence material SmB₆. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 10, 645–648 (25 November 1997)     

Quadratic Jahn-Teller effect in octahedral clusters. An interpretation of the excitation spectrum of MgO: V2+

The tunneling between tetragonal and orthorhombic stable distortions in an O_h complex is considered. The results are discussed in view of a possible interpretation of the structure of the no-phonon line (⁴A_2g→⁴T_2g) in MgO: V²⁺.     

Dynamic spin Jahn-Teller effect in small magnetic clusters

We study the effect of spin-phonon coupling in small magnetic clusters, concentrating on a S=1/2 ring of 4 spins coupled antiferromagnetically. If the phonons are treated as classical variables, there is a critical value of the spin-phonon coupling above which a static distortion occurs. This is a good approximation if the zero point energy is small compared to the energy gain due to the distortion, which is true for large exchange interactions compared to the phonon energy (J≫ħω). In the opposite limit, one can integrate out the phonon degrees of freedom and get an effective spin Hamiltonian. Using exact diagonalizations to include the quantum nature of both spins and phonons, we obtain the spectrum in the whole range of parameters and explicit the crossover between the classical and quantum regimes. We then establish quantitatively the limits of validity of two widely used approaches (one in the quantum and one in the classical limits) and show that they are quite poor for small magnetic clusters. We also show that upon reducing ħω/J the first excitation of a 4-site cluster becomes a singlet, a result that could be relevant for Cu₂Te₂O₅Br₂.     

Jahn-Teller effect on Sm3+ ions in SmB6

Electron spin resonance on samarium ions with stabilized valence Sm³⁺ is investigated in the fluctuating-valence semiconductor SmB₆, both pure and doped with the rare-earth ions Eu²⁺, Er³⁺, and Gd₃₊. The dynamic and static Jahn-Teller effects have been observed for the first time on rare-earth ions. The relation between the Jahn-Teller effect in a fluctuating-valence semiconductor and the excitonic nature of the ground state of such a semiconductor is discussed. Zh. éksp. Teor. Fiz. 115, 1860–1871 (May 1999)     

Pu+4的几何构型和Jahn-Teller效应

在Pu原子的相对论有效原子实势下,用密度泛函B3LYP方法计算得到Pu +4分子离子的6种稳定的几何构型.计算表明Pu+4的Td构型不能稳定存在,详细讨论了 Td构型的Jahn-Teller效应,讨论结果显示它们的各种畸变方式都符合群的分解原理, 从而证明Pu+4分子离子的Td构型的Jahn-Teller效应非常明显.D4h 构型也存在Jahn-Teller效应.     

An electron-paramagnetic-resonance study of the dynamic Jahn-Teller effect for Sc2+ in ZnS

Electron-paramagnetic-resonance spectra for ZnS:Sc²⁺ were observed from 1.3 K to 4.2 K. The spectra are characteristic of the dynamic Jahn-Teller effect for orbital E states.     

EPR study of the Jahn-Teller effect of Cu2+ ions in ZnGa2O4

The Jahn-Teller effect in the ZnGa₂O₄ spinel single crystal has been investigated using electron paramagnetic resonance of Cu²⁺ ions in the temperature range 110–560 K. It has been shown that copper ions occupy octahedral sites 16d in the ZnGa₂O₄ crystal with cubic symmetry O _h ⁷ (Fd-3m). At T < 560 K, the octahedra undergo tetragonal distortions (predominantly tension) and rotation around the fourfold axes by the angle θ ≈ 2.6°. The parameters of the spin Hamiltonian, which characterize the prolate (g _‖ = 2.355, g _⊥ = 2.077, A _‖ = 116 Oe, A _tp = 12 Oe) and oblate (g _‖ = 2.018, g _⊥ = 2.246, A _‖ = 75 Oe, A _⊥ = 44 Oe) octahedra, have been determined. At temperatures above 560 K, the static Jahn-Teller effect transforms into the dynamic effect and the spectrum of the magnetic resonance becomes isotropic with g = 2.116 (the experimental frequency corresponds to the X band).     

Photoacoustic investigation of the absorption edge of Cd1−x Fe x Te compounds

Summary We have measured at room temperature the photoacoustic spectra of Cd_1−x Fe _x Te(0<x<0.055) around the CdTe fundamental absorption threshold. We identified an absorption band at (1.38±0.01) eV, increasing with the Fe concentration, that we assigned to the⁵ E→³ T ₁ transition within the Fe²⁺ (3d ⁶) manifold. We observed also a broadening and a shift to higher energies of the CdTe absorption edge for increasingx. Work partially supported by the Italian Consorzio INFM and CNR through the GNSM.     

Jahn-Teller effect in low-spin Ni3+ in the LaAlO3 ceramic

This paper reports on an EPR study of LaAl_1?x Ni_xO₃ solid solutions with x≤0.12 made in the 4.2-to 300-K temperature range. In the X range, the broadening of the single EPR line with g _eff=2.148 was observed at temperatures below ～40 K. In the Q range, a slightly anisotropic EPR line with g _⊥ ^′ =2.145±0.002 and g _‖ ^′ =2.154±0.002 transforms to a rhombic-symmetry spectrum with g ₁=2.183±0.002, g ₂=2.143±0.002, and g ₃=2.118±0.002. It is shown that the observed low-temperature effects are due to the lowered symmetry of the complex under the combined action of the tetragonal Jahn-Teller distortions and of the trigonal component of the crystal field.     

Weak bands in the far-infrared spectrum of HCNO

Several weak transitions in the far-infrared spectrum of H¹²C¹⁴N¹⁶O between the (0000_v) levels with v = 2, 3, and 4 have been analyzed. Vibrational levels of improved accuracy have been calculated for both the (0000_v) series (v ≦ 5) and the (0001_v) series (v ≦ 3). For the latter, some inconsistencies in previous assignments have been removed. Two transitions from the (00020)² level have been assigned tentatively. The two lowest bands of the (0000_v) series of H¹³C¹⁴N¹⁶O have been found. Two new types of graphical plots have been used in the assignment.     

Dynamic Jahn-Teller effect in the NV(-) center in diamond

The negatively charged nitrogen-vacancy (NV(-)) center in diamond is considered to be one of the most promising solid state systems for quantum information applications. Excited states of the NV(-) center play a center role in the proposed applications. Using a combination of first-principles calculations and vibronic interaction model analysis, we establish the presence of a dynamic Jahn-Teller effect in the (3)E excited state. The calculated temperature-dependent dephasing rate for the zero phonon line as well as the splitting of the first two vibronic states are in good agreement with experiment.     

Jahn-Teller effect for the 3A2-term

The first detection of the zero-phonon line (ZPL) structure in the absorption spectrum for an optical transition between the ³T₁ and ³A₂-terms (λ = 1.3–1.5 μm) is reported for CdS:Ni crystals. An analysis of the structure shows that its occurrence is due to the weak vibronic coupling of the ³A₂-state with trigonal pseudolocal vibrations of energy hω = 22 cm⁻¹, i.e. the dynamic Jahn-Teller (JT) effect is observed. The energy of the JT coupling is E_JT = 13 cm⁻¹. With E_JT < hω, a weak JT coupling takes place. Besides the ZPL, the absorption spectrum also involves other lines of vibronic nature which can be treated as dielectric local vibration modes. An axial pressure (P) is shown to lead to a change in the magnitude of E_JT: for P ∥ C(C being the optical axis of the crystal), E_JT increases, and for P ⊥ C, it decreases.     

The substitution of Fe2+ ions by Ni2+ ions in green rust one compounds

The oxidation of Fe(OH)₂ in the presence of Cl^– or CO ₃ ^2– ions leads, in the first stage of the reaction, to chloride-containing green rust one (GR1), 3Fe(OH)₂· Fe(OH)₂Cl·nH₂O, or carbonate-containing GR1, 4Fe(OH)₂·Fe₂(OH)₄CO₃·nH₂O, respectively. These GR1 compounds give the ferric oxyhydroxides by further oxidation. If a hydroxide Ni _x Fe_1–x (OH)₂ is initially precipitated, the reaction leads to a nickelous-ferric compound isomorphous to the ferrous-ferric GR1, but stable with respect to the oxidizing action of air. Similarly, the oxidation of a nickelous-ferrous hydroxide, in the presence of excess OH^– ions, leads to a nickelous-ferric GR1, a layered hydroxide with anionic interlayers made of OH^– ions and water molecules. The Mössbauer spectra of these nickelousferric GR1 display two ferric doublets, D₀ withIS=0.34 mm/s andQS=0.45 mm/s and D₁ withIS=0.36 mm/s andQS=0.86 mm/s. The existence of a ferrous-ferric GR1 incorporating OH^– ions, a compound never observed so far, is strongly suspected.     

C2+4的几何构型和Jahn-Teller效应

用从头计算法GCISD/6-311G*得到了C2+4分子的10种不同的几何构型,基中包括Cs,C∞v,C2v,D2h,D∞h,D4h,D2d,C3v等不同的构型.计算表明C2+4的Td构型不能稳定存在,详细讲座了Td构型的Jahn-Teller效应.讨论结果显示它们的各种畸变方式都符合群的分解原理,从而证明了C2+4分子的Td构型的Jahn-Teller效应非常明显.D4构型也存在Jahn-Teller效应.     

LiNbO3∶Fe3+晶体的光谱精细结构、零场分裂参量及Jahn-Teller效应

应用不可约张量方法和群的理论构造了三角对称晶场中3d5组态离子的252阶可完全对角化的微扰哈密顿矩阵,利用该矩阵计算了LiNbO3∶Fe3+晶体的光谱精细结构、零场分裂、晶体结构、Jahn-Teller(J-T)效应,其理论计算值与实验值相符合,并研究了自旋四重态、自旋二重态分别对基态能级的影响,证明了自旋四重态对基态能级的贡献是主要的,自旋二重态对基态能级的贡献虽很小,但却是不可忽略的.在此基础上,进一步研究了自旋-轨道耦合作用、自旋-自旋耦合作用对LiNbO3∶Fe3+晶体的光谱精细结构和零场分裂参量的影响,发现自旋-轨道耦合作用是最主要的,自旋-自旋耦合作用也是不可忽略的. 研究表明,该种物质的四重态光谱结构中含有J-T效应. 其产生原因是自旋-轨道耦合及三角畸变的共同作用的结果,两者缺一不可.