Ye Hong-Juan

The screening effect of phonon modes in high-Tc oxide superconductor

This paper presents three different kinds of infrared (IR) spectra of oxide materials. The first one is the IR reflection spectra of Tl2Ba2Ca2Cu3O10 superconducting film at the incident angles 7°, 12° and 30°. The second one is the IR spectra of nonsuperconducting ceramic materials YBa2Cu3O6 and PrBa2Cu3O7. The third one is the IR spectra of superconductor YBa2Cu3O7-δ and of its film with the c-axis perpendicular to the film plane, as well as the changes in the spectra of these materials after annealing at different temperatures. It is found that in the spectra of high-Tc oxide superconductor, only the phonon modes along c-axis can be observed while the modes in a-b plane are absent. But in the spectra of nonsuperconductors the modes in a-b plane can be observed. Particularly in the absorption spectra of the semiconductor YBa2Cu3O6, all eleven allowed IR active modes have been detected. We suggest that the above experimental phenomena may result from the fact that the phonon modes vibrating in the a-b plane of the high-Tc oxide superconducting materials are almost screened by the free carriers which can move only in a-b plane.

Bond structure and electron states of charged C60

In the alkali-metal doped C60, the charge transfer induces the distortion of the bond structure and forms the self-trapping electronic bound states. Our theory manifests: 1, the charge transfer reduces the symmetry of C60 from Ih to D5d. 2, Both the bond distortion and the self-trapping states possess layer structures and are localized in the equatorial area. 3, The carbon atoms in charged C60 are divided into eight layers with an inversion center, then there exist four nonequivalent groups of carbon atoms. It makes the NMR line split into a fine structure with strength ratio 1: 1: 2: 2. 4, The charged C60 has two self-trapping bound states, one is 0.06 eV above HOMO with odd parity and the other is 0.05 eV below LUMO with even parity.

Far-infrared and infrared reflections of Tl2Ba2Ca2Cu3O10 film

The far-infrared and infrared reflection spectra of Tl2Ba2Ca2Cu3O10 superconducting film are reported in this paper. It is found there are three sharp reflection edges in both the superconducting and normal states, their positions being near ≈ 150, ≈ 350 and ≈ 600 cm-1. We attribute these reflection spectra to the Drude free carriers and a wide mid-infrared absorption band. When the incident angle increases from 7° to 30°, some additional structures appear in the reflection spectra, which are the A2u phonon modes vibrating along c-axis.

Low Frequency Impurity Vibration Modes In II-VI Semiconductor

The quasi-local modes induced by light impurities in CdTe and observed by use of the far infrared spectroscopy have been reported. The theoretical analysis of these modes by combining the Greens function with Recussion calculation has shown an obvious acoustic phonon behavior of quasi-local modes.