https://repository.library.northeastern.edu/files/neu:331186/fulltext.pdf

A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

One of the outstanding questions concerning the high-temperature superconductor YBa2Cu3O7 is the relative importance of the CuO2 planes (Cu(2) site) and the CuO chains (Cu(1) site). Many theories1,2 have stressed the importance of the 3d holes at the Cu sites, which provide an antiferromagnetic correlated background necessary for the coupling of the superconducting electrons. We have substituted Zn(3d104s2) and Ga(3d104s24p1) in the Cu(2) and Cu(1) sites, respectively, while maintaining the oxygen stoichiometry at 7. In the valence states of 2 + and 3 + respectively, the 3d bands of both elements are completely full, without the complication of a magnetic moment. Here we discuss the structural changes that accompany Zn and Ga substitution, as deduced from X-ray and neutron diffraction, and correlate these changes with the superconducting properties. We show that the integrity of the planes is much more important than that of the chains in sustaining high-Tc superconductivity.

Significance of plane versus chain sites in high-temperature oxide superconductors

Publisher Summary This chapter discusses the structural studies performed on superconducting oxides. It focuses primarily on Y 1 Ba 2 Cu 3 O 7–δ , nicknamed the 123 structure, because this structure has been the most extensively studied to date. The chapter describes the basic atomic arrangements in Y 1 Ba 2 Cu 3 O 7–δ and the way these arrangements change as a function of processing. The defects that are commonly found in the 123 structure are discussed, some of which play a dominant role in controlling superconducting properties. The studies of elemental substitutions for Y, Ba, Cu and/or O in 123 are summarized, and 123 with the other families of superconducting oxides is compared. These studies have both theoretical and practical interest because they provide clues to the roles that various structural features play in the mechanism of high-temperature superconductivity, which, in turn, may aid in the discovery of even higher temperature superconductors. It is evident from the variety of behaviors exhibited by 123 after different processing conditions that the structure has considerable flexibility. The oxygen stoichiometry can be varied over a wide range, and different cations can be substituted at least partially into every site.

The Structure of Y1Ba2Cu3O7-δ and its Derivatives

We review the specific heat measurements on La2CuO4, La2−xMxCuO4 (M = Ca, Sr, and Ba), YBa2Cu3O7, and the Bi-Ca-Sr-Cu-O and Tl-Ca-Ba-Cu-O systems. Tables of properties derived from the data are presented. Results on RBa2Cu3O7 (R=rare earth elements other than Y) are summarized, as are results on YBa2(Cu3−xMx)O7 (M=Zn, Cr, Fe, or Ni). The difficulties of analyzing the specific heat data, and specifically the separation of the contributions associated with magnetic impurities, are discussed. It is tentatively concluded that the data nearT

 c
 are consistent with BCS theory, although they show evidence of fluctuation effects. It is also concluded that the low-temperature zero-field data on a majority of the high-T

 c
 oxide superconductors provide evidence of anintrinsic term that is proportional toT, a result that is inconsistent with a gap in the electronic density of states.

Specific heat of the high- T c oxide superconductors

An experimental study is presented of Y-Ba-Cu-O/Ag composites employing a variety of different experimental techniques: electrical transport, magnetometry, light and electron microscopy, electron microprobe analysis, X-ray diffractometry, and X-ray absorption. Three different distinct chemical environments for Ag in such composites are identified. The nature of the chemical interactions of Ag and YBa 2 Cu 3 O 7− x and the benefits of the inclusion of silver are discussed in terms of these results.

Y-Ba-Cu-O/silver composites: An experimental study of microstructure and superconductivity

Many electron-paramagnetic-resonance (EPR) and magnetic susceptibility measurements for the high-Tc superconductors of the form RBa2Cu3O9-x (R=Y or a rare earth) have been reported. Excluding local moment resonances due solely to the R atoms, we show that all of the EPR measurements known to us are not intrinsic to the superconducting phase, but rather are due to low concentrations of spurious phases typically present in the samples. BaCuO2 is found to be the main source of the low-temperature EPR signal and of the magnetic susceptibility which has been reported for YBa2Cu3O9-x above Tc. © 1987 The American Physical Society.

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Precautions when interpreting EPR and dc magnetization measurements of high-Tc RBa2Cu3Oy-phase superconducting materials.

https://escholarship.org/content/qt1w81d8f0/qt1w81d8f0.pdf?t=oam78p

Electron paramagnetic resonance, electrical resistivity, and magnetization studies in the high Tc superconductors EuBa2Cu3O9−xandEuBa2 (Cu1−yMy)3O9−x (M = Cr, Mn, Fe, Co, Ni, ORZn)

After years of searching for superconductors with higher transition temperatures, an incredible success has been achieved in recent months, as a consequence of the discovery of Bednorz and Muller of a 30 K transition in La2-yBayCuO4-x,1 followed by the subsequent findings that YBa2Cu2O9-x has a Tc well above liquid nitrogen temperatures.2,3 These discoveries have resulted in an explosive growth of interest in the field, with the present challenge being to explain the pertinent superconducting mechanisms.

EPR, Magnetization, and Resistivity Studies in DOPED (4f, 3d Ions) and Undoped R (or Y) Ba2Cu3O9−x High Tc Superconductors

We have measured electron paramagnetic resonance (EPR), resistivity, and dc susceptibility from 2 to 300 K for the oxide high Tc superconductors (R)Ba2Cu3Oy (R=Y,Pr,Nd,Eu,Gd,Ho,Er,Tm, or Yb). Selected systems were doped with 3‐d ions (Cr,Mn,Fe,Ni,Co, or Zn) or 4‐f ions (Gd or Er) which presumably substitute for the Cu or R site, respectively. In the systems studied we have observed an EPR line at low temperatures (T<40 K), which exhibits an increase in intensity and decrease in field for resonance as the temperature is lowered. The ESR linewidth is also temperature dependent and exhibits a minimum at about 15 K. An additional EPR line that can be associated with a Gd3+, Mn2+ or Er3+ ion was observed for those samples where these ions were present as dilute impurities. In some of the samples another EPR signal is observed with properties that depend on sample preparation conditions. The behavior and origin of all lines will be discussed. The variation of Tc with concentration of the added impurities over t...

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EPR, magnetization, and resistivity studies in doped (4‐f or 3‐d ions) and undoped RBa2Cu3Oy high TC superconductors (R=Y,Pr,Nd,Eu,Gd,Ho,Er, or Yb) (abstract)

J. F. Smyth

Papers

Precautions when interpreting EPR and dc magnetization measurements of high-Tc RBa2Cu3Oy-phase superconducting materials.

Electron paramagnetic resonance, electrical resistivity, and magnetization studies in the high Tc superconductors EuBa2Cu3O9−xandEuBa2 (Cu1−yMy)3O9−x (M = Cr, Mn, Fe, Co, Ni, ORZn)

EPR, Magnetization, and Resistivity Studies in DOPED (4f, 3d Ions) and Undoped R (or Y) Ba2Cu3O9−x High Tc Superconductors

EPR, magnetization, and resistivity studies in doped (4‐f or 3‐d ions) and undoped RBa2Cu3Oy high TC superconductors (R=Y,Pr,Nd,Eu,Gd,Ho,Er, or Yb) (abstract)