The temperature-dependent structural changes were investigated by using the X-ray diffraction and the Extended X-ray absorption fine spectroscopy (EXAFS) for layered perovskite manganites La2-2xSr1+2xMn2O7 (x=0.33 and 0.4). The anomalous changes of Mn-O bond length and Jahn-Teller (J-T) distortion of MnO6 octahedron were observed, corresponding to ferromagnetic transition temperature (~ 120 K)....

The nature of the magnetic state of LiNiO2 has been controversial. In this compound Ni spins sS=1/2d form a triangular lattice with the possibility of magnetic frustration, but the exact state of spin correlation has not yet been known in spite of the extensive research work. A factor that complicates understanding of the magnetic state is the orbital state of Ni3+ which is a Jahn-Teller sJTd i...

The thermodynamic theory of second order phase transitions in crystals with the modifications and simplifications recently made by the author and co-workers is applied to the rocksalt structure. We predict several lower symmetry phases achievable via second-order displacive transitions which do not change the unit cell, in addition to the trigonal structure seen in GeTe. A microscopic model is ...

We discuss how orbital degeneracy, which is usually removed by a cooperative Jahn-Teller distortion, could under appropriate circumstances lead rather to a Resonating Valence Bond spin-orbital liquid. The key points are: i) The tendency to form spin-orbital dimers, a tendency already identified in several cases; ii) The mapping onto Quantum Dimer Models, which have been shown to possess Resonat...

Using a microscopic 1 p a r t i c l e 1 hole doorway model fo r nuclear exci ted states we show that the continuous forward angle energy spectra of medium energy (p .n) react ions are mainly a resu l t of d i rec t one-step processes. The model is appl ied to the reactions Ca(p,n) at 160 MeV and to 9 0 Zr (p ,n ) at 200 MeV incident energy. In case of 9 0 Zr (p ,n ) we f i nd that a large f r a...

Photon-added Gazeau-Klauder and Klauder-Perelomov coherent states are investigated. Application to Pöschl-Teller potentials is given.

We comment on a recent paper by Chen, Liu, and Ge (J. Phys. A: Math. Gen. 31 (1998) 6473), wherein a nonlinear deformation of su(1,1) involving two deforming functions is realized in the exactly solvable quantum-mechanical problem with Pöschl-Teller potential, and is used to derive the well-known su(1,1) spectrum-generating algebra of this problem. We show that one of the defining relations of ...

The doped cuprates are considered to be a system of local spinless bosons moving in a lattice of the hole pseudo-Jahn-Teller centers CuO 4 . A detailed qualitative and quantitative description of the vibronic mechanism determining both the isotope substitution and the external pressure effect on Tc is given. This mechanism can properly interpret the principal peculiarities of isotopic and baric...

We report Extended X-Ray Absorption Fine Structure measurements at the Mn K absorption edge on hole doped manganese oxides La1ÿxCaxMnO3 in a wide temperature range above and below the metal±insulator transition temperature in presence of a magnetic field. In accordance with previous studies an anomalous increase in the Debye-Waller factors is detected at the phase transition in the first coordi...

This paper presents a new concept of algorithms for estimation of maximum frequency ( fmax) in the nonstationary Transcranial Doppler (TCD) signal. The improvement of estimator’s properties is achieved by exploiting the knowledge about dynamic properties of the blood flow. The raw estimates of fmax, calculated with a conventional algorithm for short segments of TCD signal, are smoothed and used...