Showing papers by "Bertram Batlogg published in 1988"

Thermally activated dissipation in Bi2.2Sr2Ca0.8Cu2O8+δ

Abstract: A new dissipation behavior is reported in superconducting Bi2.2Sr2Ca0.8Cu2Oa+δfor all temperatures belowTc and all magnetic fields exceeding Hc1. The current-independent electrical resistivity is thermally activated and can be described by an Arrhenius law with a single prefactor and a magnetic-field-and orientation-dependent activation energyU 0 (H,o).This behavior is markedly different from past observations and will be discussed in terms of flux creep and flux flow. This thermally activated behavior implies a finite resistance at all temperatures and all fields exceeding H c1 determined by the activation energy as the only parameter.

Structure and physical properties of single crystals of the 84-K superconductor Bi 2.2 Sr 2 Ca 0.8 Cu 2 O 8+δ

Abstract: Single crystal sof the 84-K superconductor ${\mathrm{Bi}}_{2.2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{0.8}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ were characterized by x-ray diffraction, dc magnetic susceptibility, electrical resistivity, and microwave absorption. The structure has ${[\mathrm{Cu}{\mathrm{O}}_{2}]}_{\ensuremath{\infty}}$ planes separated by calcium atoms, edge-shared bismuth oxide double layers, and an incommensurate superlattice along $b$ with a period of 4.76. The in-plane resistivity above ${T}_{c}$ is linear in $T$, with ${\ensuremath{\rho}}_{\mathrm{RT}}=130$ \ensuremath{\mu}\ensuremath{\Omega} cm. Initial results on Pb substitution yielding ${T}_{c}'\mathrm{s}$ of 107 K are reported.

Superconductivity near 70 K in a new family of layered copper oxides

Abstract: A new family of high-temperature superconductors is described, with the general formula Pb2Sr2ACu3O8+δ. Although they have the planes of CuO5 square pyramids characteristic of the other copper-oxide superconductors, the new compounds belong to a distinct structural series, with wide scope for elemental substitution. Their unusual electronic configuration also gives new insight into the role of charge distribution among the structural building blocks in controlling superconductivity.

Growth of superconducting single crystals in the Bi-Sr-Ca-Cu-O system from alkali chloride fluxes

Abstract: The discovery of superconductivity at temperatures above the boiling point of nitrogen has led to intense interest in the physics and chemistry of materials exhibiting this behaviour. Although some experiments can be performed on sintered polycrystalline samples, large single crystals are important for many measurements of physical properties, including investigations of the relationship between structural parameters and superconducting properties. Like its predecessors YB2Cu3O7 (refs 1–4) and La2–xSrxCuO4 (ref. 5), the recently discovered 84-K bismuth–strontium–calcium cuprate superconductor6–9 melts incon-gruently, and crystals have been grown from eutectic melts10. This technique yields crystals large enough for some experiments, but is generally difficult to control, placing limits on the size of crystals that can be grown. In addition, the crystals must be mechanically separated from the melt. Here we report the growth of single crystals of Bi2.2Sr2Ca0.8Cu2O8+δ from alkali chloride fluxes. The crystals are superconductors, showing large Meissner effects and zero-resistance transitions above 80 K. Flux growth is a standard high-temperature solution growth technique, and should allow crystal size and quality to be controlled by parameters such as equilibration temperature, cooling rate and melt composition. The fluxes reported here are easily washed from the crystals.

Diffraction evidence for oxygen-vacancy ordering in annealed Ba 2 YCu 3 O 7 − δ (0.3 ≲δ≲ 0.4) superconductors

Abstract: Diffuse streaks centered at q=(0,\ifmmode\pm\else\textpm\fi{}(2/5,0) and (0,\ifmmode\pm\else\textpm\fi{}(1/2,0) have been observed in annealed ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ with 0.3\ensuremath{\lesssim}\ensuremath{\delta}\ensuremath{\lesssim}0.4, which has a ${T}_{c}$ of 60 K and a Meissner effect equivalent to the 90 K phase. We interpret the presence of the diffuse streaking as a result of short-range oxygen vacancy ordering. The vacancy ordering has a short correlation length along the copper-oxygen chains (b direction) and a long correlation length perpendicular to the chains along the a direction. The ordered structure is completely uncorrelated parallel to the c axis.

X-ray-scattering study of finite-range order in Ba2YCu3O6.7.

Abstract: We have observed evidence of finite-range order in quenched crystals of nominal composition ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{6.7}$. X-ray scattering shows diffuse peaks with a reduced wave vector of (1/2,0,0) in the oxygen-deficient compound but not in fully oxidized ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{7}$. Although the crystals are twinned, we find that the diffuse satellites occur symmetrically around (h,0,0) peaks rather than (0,k,0) peaks indicating a doubling of the unit cell along the a axis (transverse to the Cu-O chains). The width of the diffuse peaks yields coherence lengths of 21, 16, and 9 A\r{} for the ${a}_{0}$, ${b}_{0}$, and ${c}_{0}$ directions, respectively.

Superconducting and normal state parameters of Bi2.2Sr2Ca0.8Cu2O8+δ single crystals: A comparison with Ba2YCu3O7

Abstract: Magnetic and magnetotransport properties were studied on Bi 2.2 Sr 2 Ca 0.8 Cu 2 O 8+δ single crystals. The normal state resistivity in the a-b plane varies linearly with temperature and extrapolates to zero at T = 0. The slopes of the upper critical field are −4.5+1(−0.55) T/K for H perpendicular (parallel) to the c-axis. The coherence length is calculated to be ≈30A˚in the a-b plane but only ≈A˚perpendicular to it. ξ c is thus shorter than the 12A˚spacing between the Cu-O double layers. From H c1 and H c2 data, the Sommerfeld parameter γ is deduced.

Batlogg, Cava, and Stavola reply.

Abstract: A reply to the comment on oxygen isotope effect in high temperature YBaCuO perovskite uperconductors is presented. (AIP)