Phonon screening in high-temperature superconductors

In good conductors optical phonons are usually screened, and therefore not observed. However, sharp features due to infrared-active modes in the copper-oxygen planes are observed in the optical conductivity of Pr1.85Ce0.15CuO4 and YBa2Cu3O6.95. Oscillator strengths indicate that the screening of these modes is poor or totally absent. These materials are compared with eta-Mo4O11, in which lattice modes appear suddenly below the charge-density wave transition. It is proposed that poor screening in the cuprates originates from fluctuating charge inhomogeneities in the copper-oxygen planes.     

Intermediate coupling model description of55Fe and57Fe

The properties of the negative parity states of⁵⁵Fe and⁵⁷Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states.     

Photoluminescence and infrared absorption studies of Ge doped with Mg

The photoluminescence spectrum of Ge doped with the double acceptor Mg reveals lines due to both bound excitons and bound multiexciton complexes, which are in some ways similar to those previously reported for Ge:Be and Ge:Zn. As in Ge:Zn, the Ge:Mg bound exciton line was found to be a doublet, showing that the Mg double acceptor in Ge also has a split ground state. Further evidence for this ground state splitting is found from the temperature dependence of the infrared absorption spectrum of the Mg double acceptor.     

Updated tables of parameters of (T,M, S)-nets

We present an updated survey of the known constructions and bounds for (t, m, s)- nets as well as tables of upper and lower bounds on their parameters for various bases. © 1999 John Wiley & Sons, Inc. J. Cobin Designs 7: 381–393, 1999