Enhanced Superconductivity in Sr2CuO4-v

A critical review of previous investigations of the superconductivity with enhanced Tc ~ 95K found in Sr2CuO4-v shows that new physics occurs in a highly overdoped region of the cuprate phase diagram. Moreover, evidence is adduced from the literature that 30% of the oxygen sites in the CuO2 layers are vacant, a conclusion which is at odds with the universally made assumption that superconductivity originates in stoichiometric CuO2 layers. While further research is needed in order to identify the pairing mechanism(s) responsible for the enhanced Tc, we suggest possible candidates

Phonon-drag effects on thermoelectric power

We carry out a calculation of the phonon-drag contribution $S_g$ to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to the weakly nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation times due to phonon-phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at high temperatures. In the linear transport limit, $S_g$ is equivalent to the result obtained from the Boltzmann equation with a relaxation time approximation. The theory is applied to experiments and agreement is found between the theoretical predictions and experimental results. The role of hot-electron effects in $S_g$ is discussed. The importance of the contribution of $S_g$ to thermoelectric power in the hot-electron transport condition is emphasized.Comment: 8 pages, REVTEX 3.0, 7 figures avilable upon reques

Thermoelectric power of nondegenerate Kane semiconductors under the conditions of mutual electron-phonon drag in a high electric field

The thermoelectric power of nondegenerate Kane semiconductors with due regard for the electron and phonon heating, and their thermal and mutual drags is investigated. The electron spectrum is taken in the Kane two-band form. It is shown that the nonparabolicity of electron spectrum significantly influences the magnitude of the thermoelectric power and leads to a change of its sign and dependence on the heating electric field. The field dependence of the thermoelectric power is determined analytically under various drag conditions.Comment: 25 pages, RevTex formatted, 3 table

High-energy neutron irradiation of superconducting compounds

The effect of high-energy neutron irradiation (E greater than 1 MeV) at ambient reactor temperatures on the superconducting properties of a variety of superconducting compounds is reported. The materials studied include the A-15 compounds Nb$sub 3$Sn, Nb$sub 3$Al, Nb$sub 3$Ga, Nb$sub 3$Ge and V$sub 3$Si, the C-15 Laves phase HfV$sub 2$, the ternary molybdenum sulfide Mo$sub 3$Pb$sub 0$.$sub 5$S$sub 4$ and the layered dichalcogenide NbSe$sub 2$. The superconducting transition temperature has been measured for all of the above materials for neutron fluences up to 5 x 10$sup 19$ n/cm$sup 2$. The critical current for multifilamentary Nb$sub 3$Sn has also been determined for fields up to 16 T and fluences between 3 x 10$sup 17$ n/cm$sup 2$ and 1.1 x 10$sup 19$ n/ cm$sup 2$. (auth

The phase diagram of NiSi under the conditions of small planetary interiors

The phase diagram of NiSi has been determined using in situ synchrotron X-ray powder diffraction multi-anvil experiments to 19 GPa, with further preliminary results in the laser-heated diamond cell reported to 60 GPa. The low-pressure MnP-structured phase transforms to two different high-pressure phases depending on the temperature: the ε-FeSi structure is stable at temperatures above ∼1100 K and a previously reported distorted-CuTi structure (with Pmmn symmetry) is stable at lower temperature. The invariant point is located at 12.8 ± 0.2 GPa and 1100 ± 20 K. At higher pressures, ε -FeSi-structured NiSi transforms to the CsCl structure with CsCl-NiSi as the liquidus phase above 30 GPa. The Clapeyron slope of this transition is -67 MPa/K. The phase boundary between the ε -FeSi and Pmmn structured phases is nearly pressure independent implying there will be a second sub-solidus invariant point between CsCl, ε -FeSi and Pmmn structures at higher pressure than attained in this study. In addition to these stable phases, the MnP structure was observed to spontaneously transform at room temperature to a new orthorhombic structure (also with Pnma symmetry) which had been detailed in previous ab initio simulations. This new phase of NiSi is shown here to be metastable

Model for superconductivity in optimally doped electron cuprates

The very anomalous normal state properties and superconductivity of electron-doped supercon-ducting cuprates with the T* structure are discussed. The literature values of high mobilities for electrons and holes are explained by the electrons and holes existing in different layers. The annealing procedures necessary for superconductivity produce oxygen-vacancy negative-U pairing centers. The relative insensitivity of Tc to the annealing condition is attributed to stabilization of the chemical potential near the middle of the narrow oxygen band formed by oxygen vacancies where the electronic entropy is large

The high T/sub c/ superconducting bolometer

A description is given of the optimization of a bolometric infrared detector which uses the resistive transition of a high T/sub c/ film as the thermometer. The performance of a LN cooled far infrared bolometer operated with a cooled low-pass filter is computed for the ideal case of a noise-free readout. The theory is then extended to include various contributions to the readout noise. Measurements are presented of the low frequency noise near T/sub c/ in current biased films of ErBa/sub 2/Cu/sub 3/O/sub 7/, which show that useful performance can be achieved. Comparisons are made with other infrared detection technologies which show that practical high T/sub c/ bolometers will be especially useful for wavelengths longer than the /approximately/20 ..mu..m cutoff of LN cooled photovoltaic detectors. Potential applications include far infrared laboratory spectroscopy and passively cooled space observations of bright sources such as the earth. 6 refs., 3 figs

Thermally activated flux motion in <i>a</i>-axis YBa₂Cu₃O₇/PrBa₂Cu₃O₇ superlattices

We have investigated resistive properties of a-axis YBa₂Cu₃O₇/a,b-axis PrBa₂Cu₃O₇ superlattices in magnetic fields to study thermally activated flux-flow resistance. We find that in magnetic fields perpendicular to the YBa₂Cu₃O₇/PrBa₂Cu₃O₇ layering the activation energies of these superlattices deduced from the tail of the resistive transitions have a logarithmic magnetic-field dependence for small YBa₂Cu₃O₇ thicknesses (<300 Å), in agreement with recent theories of thermally activated resistance in strongly pinned two-dimensional superconductors