Resistivity, thermopower and single-particle tunneling studies on some zinc-doped yttrium barium copper oxide superconductors
TL;DR: In this article, the average dimension of the Josephson junction is estimated to be a few tens of A, suggesting the microtwin boundaries to be the location of the junctions.
Abstract: Resistance and thermopower measurements have been made on a series of compounds, YBa2Cu3- x Zn x O7-y, with x = 0.025, 0.05, 0.1, 0.15 and 0.2. The superconducting transition temperature decreases as the zinc concentration increases. In a range of temperatures below TM , the mid point of the transition, the resistance shows an exponential temperature dependence fitting the phenomenological formula proposed by Ausloos et al. From the plot of logarithm of resistivity vs. (TM ‒ T) 1/2/T, one deduces a value of the average dimension of the Josephson junction to be a few tens of A, suggesting the microtwin boundaries to be the location of the junctions. The thermopower shows a peak always just above Tc . This conclusively shows that phonon drag is not the cause of the peak. The temperature dependence of the thermopower appears to resemble closely the earlier observations of Srinivasan et al. on yttrium barium copper oxide. Single-particle tunneling measurements carried out for two concentrations, x = ...
References
More filters
TL;DR: In this paper, the origin of the orthorhombic-tetragonal transition and the importance of the Cu-O chains for superconductivity is discussed. But the behavior of these materials with respect to magnetic impurities is apparently different from conventional Bardeen-Cooper-Schrieffer-type superconductors, and any new mechanism proposed must be mostly sensitive to local structural disorder.
Abstract: The mixed ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{M}}_{\mathrm{x}}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{y}}$ (M=Ni, Zn, Fe, Co, and Al) phases have been characterized for their structural, magnetic, and superconducting properties. The oxygen content in these phases is dependent on the nature and the amount of doping, especially for Co and Fe. The material remains orthorhombic when Cu is replaced by Ni or Zn whereas it evolves to tetragonal symmetry for the Fe-, Co-, and Al-doped compounds when x exceeds 0.05. Evidence for the major substitution of Co in the Cu-O chains only is obtained by means of thermogravimetric analysis and neutron diffraction measurements. The room-temperature M\"ossbauer spectra of the Fe-doped compounds consist of three doublets; their site assignments are proposed. dc resistance and ac susceptibility have shown that both magnetic and diamagnetic ions destroy ${T}_{c}$ in a similar manner. At x=0.2 the Fe and Co compounds are tetragonal, superconduct at 50 K, and show a Curie-type magnetic behavior associated with a magnetic moment of 3.4${\ensuremath{\mu}}_{B}$ per doping atom. The origin of the orthorhombic-tetragonal transition and the importance of the Cu-O chains for superconductivity is discussed. The behavior of these materials with respect to magnetic impurities is apparently different from conventional Bardeen-Cooper-Schrieffer-type superconductors, and we believe that any new mechanism proposed must be mostly sensitive to local structural disorder.
670 citations
TL;DR: The superconducting state was investigated by both resistance and magnetization measurements and the magnetic susceptibility above T/sub c/ was found to be strongly correlated with the size of the paramagnetic moments, largely due to scattering from the magnetic sites.
Abstract: We have fabricated samples of the form ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{0.9}$${\mathrm{A}}_{0.1}$${)}_{3}$${\mathrm{O}}_{6+\mathrm{y}}$ where A=Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The superconducting state was investigated by both resistance and magnetization measurements. In addition, the magnetic susceptibility above ${T}_{c}$ has been measured. ${T}_{c}$ was found to be strongly correlated with the size of the paramagnetic moments, largely due to scattering from the magnetic sites. In the sample containing Zn, however, ${T}_{c}$ was dramatically reduced due to filling of the antibonding d band.
366 citations
TL;DR: In this article, the authors measured the thermal conductivity, thermopower, Hall constant, and resistivity of a Y${T}_{c}$ superconductor, and ascribe to an increase in lattice conduction due to a reduction in the scattering of phonons by holes.
Abstract: We have measured the thermal conductivity, thermopower, Hall constant, and resistivity of a Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ high-${T}_{c}$ superconductor. The thermal conductivity shows a striking increase below the transition temperature ${T}_{c}$, which we ascribe to an increase in lattice conduction due to a reduction in the scattering of phonons by holes as superconducting pairs form. This property, and the others we have measured, are consistent with ordinary metallic conduction mechanisms with short phonon and carrier free paths, and a strong interaction of phonons with a small density of hole carriers.
154 citations
TL;DR: In this paper, the structural and superconducting properties of the high Tc compound YBa2Cu3(1−x)M3xO7−δ have been performed where M = Ag, Li, Pt, Zn, Cr, Mn, Fe, Co, Ni and x = 5 or 10 %.
Abstract: A systematic study of the structural and superconducting properties of the high Tc compound YBa2Cu3(1−x)M3xO7−δ has been performed where M = Ag, Li, Pt, Zn, Cr, Mn, Fe, Co, Ni and x = 5 or 10 %. X-ray powder diffraction, a.c. susceptibity and resistivity measurements have been made. Most substitutions do not significantly modify the YBa2Cu3O7 cell parameters, with the exception of Fe and Co, which stabilize a tetragonal cell similar to that of YBa2Cu3O<6.6 (but with a smaller c-parameter), even for high oxygen contents (δ ≈ 0). The magnetic character of the impurity appears to strongly decrease Tc in the case of Fe and Co. However some non-magnetic impurities like Li or Zn also have a strong effect on the superconducting properties. This indicates that disorder plays an important role in the superconductivity. Superconducting phases with Tc (onset) of 70 K and 50 K are often detected, which might correspondsto a preferential substitution on particular sites. Moreover, the oxygen content of the samples (annealed in oxygen) seems to vary with M, which is another explanation of the observed effects.
79 citations
TL;DR: In this article, the thermoelectric power of Y1Ba2Cu3O7−y has been precisely measured in absence of, but also under applied (small) magnetic fields over a large temperature range [65 −230 K].
Abstract: The thermoelectric power (TEP) of Y1Ba2Cu3O7−y has been precisely measured in absence of, but also under applied (small) magnetic fields over a large temperature range [65–230 K]. The thermoelectric power is positive for all field values. The knee observed on the magneto-resistivity below the so-called “critical temperature” is observed here as well. An anomalous hysteresis is found. The temperature derivative of the TEP at Tc is analyzed on a log-log plot. Discussion of the peak above Tc, and of the sometimes observed negative dip below Tc is presented.
38 citations