[en] The interactions between Teller, Renner, Jahn and Landau which led to the formulation of the Jahn-Teller effect are discussed. The applicability of Jahn-Teller type of theory to superconductivity and the explanation proposed by the use of Goldstone particles are assessed

No abstract available

[en] Within a revival of interest in the emission properties of Tl⁺-like impurity centers in alkali-halide crystals, the problem of a complete interpretation of high-energy and low-energy emissions in the A-band of KCl:Tl remains without a satisfactory explanation. Two previous works reported experimental results relative to spectral and decay-time measurements for low-energy (weak) emission at 475 nm, and for high-energy emission at 300 nm. In the latter case, however, a confirmation of the existence of an anomalous type of behavior in the slow decay time needed to be clarified. The results reported here demonstrate that this anomaly is not present in high-energy emission. On the basis of these more recent experimental results, an attempt is made to obtain a unifying model, one always based on the Jahn–Teller effect, which could serve in interpreting both high- and low-energy emissions.

[en] Published in summary form only

[en] In this work, we derive expansion formulas up to arbitrary order in vibrational coordinates for the tetrahedral and octahedral vibronic Hamiltonians that involve A-type states and a-type vibrations. The root-branch approach and modularized approach enable us to derive vibronic Hamiltonians including up to two vibrational modes for 5 problems in T symmetry and 92 problems in $T_d$ symmetry within one paper. These formulas can be easily adapted to problems of $T_h,O$, and $O_h$ symmetries. Finishing this work, we have derived general vibronic Hamiltonians for all unimodal and bimodal Jahn-Teller and pseudo-Jahn-Teller problems of cubic group systems. These bimodal formulas can be extended to cover problems that involve more than two modes.

[en] Instead of the Cooper pair of BCS theory, the authors incorporate the chemical structural effects of pairwise movement by using geminals (two-electron wavefunctions), rather than the simple orbital (one-electron wavefunction) model. Instead of the nearest-neighbor antisymmetric-type vibronic interaction of Bipolaron Theory, the authors emphasize the distant neighbor's opposing vibrations in doped systems. Besides the Jahn-Teller effect of second-order energy, the authors propose Renner-Teller effect for crystals other than linear molecules, and obtain first-order energy of degenerate vibronic geminal states by using the Herzberg-Teller expansions of vibronic states of the Hamiltonian

[en] Some characteristics of silicon divacancy as a radiation bistable defect, subject to effect of Jahn-Teller are analysed. As follows from literary sources, the adiabatic potential of silicon divacancy has two minimums, divided by high enough potential barrier that provides stability of this defect at room temperature. The presence of the strong vibronic link means that energy of Jahn-Teller stabilization is much more than energy of zero vibrations, therefore in minimums of adiabatic energy there are local vibration states. If the potential barrier appears transparent enough, there is a splitting level on which there is an vibration quantum and system can make the pulsing oscillation caused by tunnel transitions between configurations of minimums of adiabatic potential. The various percentage ratio of divacancy, having the basic minimum in one of two possible configurations is experimentally observed, for p-Si and n-Si. We, on the basis of the analysis conducted in work, offer the following interpretation of observable dependence: the states of divacancy are not independent, and are in superposition, define the equation resulted in work, describing probability of finding of the system in each of the states. In accordance with such interpretation, it means that all divacancy in this material are identical in relation to configurations of minimums, but thus minimums are not equivalent. It is shown also, that depending on external influence, properties of material, concentration of the entered defects and a kind of an irradiation can purposefully influence on the parameters of divacancy, which specifies on possibility of application of silicon with such centers for creation of devices of the quantum informative systems. (authors)

[en] Within the framework of the pair potential approximation and the shell model including the Jahn-Teller contribution to the crystal energy we have studied the elastic properties of La₂CuO₄. The strong anisotropic correlation between the lattice deformations e_xx and e_zz and the internal displacements of the accompanying sublattices within the La₂O₂ layers are shown to be responsible for the giant anisotropy of the elastic moduli in the xz-plane. We have predicted the softening of several elastic moduli in the orthorhombic phase region near the pressure-induced structural phase transition. But we have not observed the softening of c₁₁, c₁₂, and c₆₆ in the tetragonal phase region that was measured near the temperature-induced structural phase transition. (author)

[en] Polymicrocrystals of ferric borate were studied by NGR as a function of temperature up to the point where they react with the carbon packing material to form an iron carbide. The variation of the line width shows a sudden decrease at 551K which is interpreted as arising from a coherent tunnel effect between two Jahn-Teller distortions

No abstract available