40 research outputs found
Magnetic field dependence of the temperature derivative of resistivity: a probe for distinguishing the effects of pseudogap and superconducting fluctuations in cuprates
We have studied the magnetic field dependence of the temperature derivative
of the resistivity, dr(H,T)/dT, of a number of Y1-xCaxBa2(Cu1-yZny)3O7-d
crystalline thin films over a wide range of sample compositions. From the
analysis of the temperature derivative data we have been able to distinguish
quite clearly between two characteristic temperature scales, (a) the onset of
strong superconducting fluctuation temperature, Tscf and (b) the pseudogap
temperature, TPG. Significantly different characteristic features of dr(H,T)/dT
at Tscf and at TPG imply that Tscf and TPG have different physical origins.Comment: Submitted to Physica C (M2S-HTSC 2006 Proceedings
Effects of Zn on the grain boundary properties of La2-xSrxCu1-yZnyO4 superconductors
The properties of the grain boundaries (GBs) are of significant importance in
high-Tc cuprates. Most large scale applications of cuprate superconductors
involve usage of sintered compounds. The critical current density and the
ability to trap high magnetic flux inside the sample depend largely on the
quality of the GBs. Zn has the ability to pin vortices but it also degrades
superconductivity. In this study we have investigated the effect of Zn impurity
on the intergrain coupling properties in high-quality La2-xSrxCu1-yZnyO4
sintered samples with different hole concentrations, p (\equiv x), over a wide
range of Zn contents (y) using field-dependent ac susceptibility (ACS)
measurements. The ACS results enabled us to determine the superconducting
transition temperature Tc, and the temperature Tgcp, at which the randomly
oriented superconducting grains become coupled as a function of hole and
disorder contents. We have analyzed the behavior of the GBs from the systematic
evolution of the values of Tgcp(p, y), Tc(p, y), and from the contribution to
the field-dependent ACS signal coming from the intergrain shielding current. Zn
suppresses both Tc and Tgcp in a similar fashion. The hole content and the
carrier localization due to Zn substitution seem to have significant effect on
the coupling properties of the GBs. We have discussed the possible implications
of these findings in detail in this article.
PACS: 74.72.Dn; 74.62.Dh; 74.25.Sv Keywords: Zn doped La214; Critical current
density; Grain boundaryComment: To appear in Physica
Effect of the pseudogap on the uniform magnetic susceptibility of Y1-xCaxBa2Cu3O7-d
The effects of planar hole content, p, on the temperature-dependent uniform
(q = 0) magnetic susceptibility, c(T), of polycrystalline Y1-xCaxBa2Cu3O7-d
compounds with 0.0 </= x </= 0.20 were investigated over a wide range of oxygen
deficiency (d). Systematic variations in c(T) were found with changing p. The
characteristic pseudogap temperature scale, Eg(p)/kB, was extracted from the
analysis of the c(T,p) data. We have found clear evidence that the pseudogap in
the quasi-particle spectral weight appears abruptly at a planar hole content of
p ~ 0.19, and that it grows rapidly with decreasing p.Comment: Submitted to Physica C (M2S-HTSC 2006 Proceedings
Low-temperature critical current of Y1-xCaxBa2Cu3O7-delta thin films as a function of hole content and oxygen deficiency
The effects of hole content (p) and oxygen deficiency (delta) on the
zero-field critical current density, Jc0, were investigated for high-quality
c-axis oriented Y1-xCaxBa2Cu3O7-delta (x = 0, 0.05, 0.10, and 0.20) thin films.
Ca was used to introduce hole carriers in the CuO2 planes, independent of the
oxygen deficiency in the CuO1-delta chains. Low-temperature Jc0(16K) of these
films above the optimum doping were found to be high (> 10^7 Amp/cm^2) and were
primarily determined by the hole concentration, reaching a maximum at p ~
0.185+/-0.005, irrespective of oxygen deficiency. This implies that oxygen
disorder plays only a secondary role and the intrinsic Jc0 is mainly governed
by the carrier concentration and consequently by the superconducting
condensation energy which also peaks at p ~ 0.19 where the pseudogap
correlation vanishes
The Isotope Effect in Superconductors
We review some aspects of the isotope effect (IE) in superconductors. Our
focus is on the influence of factors not related to the pairing mechanism.
After summarizing the main results obtained for conventional superconductors,
we review the effect of magnetic impurities, the proximity effect and
non-adiabaticity on the value of the isotope coefficient (IC). We discuss the
isotope effect of and of the penetration depth . The theory is
applied to conventional and high- superconductors. Experimental results
obtained for YBaCuO related materials (Zn and
Pr-substituted as well as oxygen-depleted systems) and for
LaSrCuO are discussed.Comment: 31 pages, 10 figures. Review article to appear in "Pair Correlation
in Many Fermions Systems", Plenum Press 199
On the pseudogap and doping-dependent magnetic properties of La2-xSrxCu1-yZnyO4
The effects of planar hole content, p (= x), on the uniform (q = 0) magnetic
susceptibility, c(T), of La2-xSrxCu1-yZnyO4 were investigated over a wide range
of Sr (x) and Zn (y) contents. A strongly p-dependent Zn-induced magnetic
behavior was observed. The apparent Zn-induced magnetic moment is larger in
underdoped La2-xSrxCu1-yZnyO4 and it decreases quite sharply around p ~ 0.19.
It does not change much for further overdoping. This indicates a possible role
of the pseudogap on the Zn induced magnetic behavior, as there is growing
evidence that pseudogap vanishes quite abruptly at p ~ 0.19.Comment: Submitted to Physica C (Proceedings of the M2S-HTSC-VIII Conference
The effect of Zn substitution on the state of oxygen deficiency and hole concentration in Y1-xCaxBa2(Cu1-yZny)3O7-d
We have investigated the effect of Zn substitution on the hole content, p,
and the oxygen deficiency, d, for a series of high-quality crystalline c-axis
oriented thin films and polycrystalline Y1-xCaxBa2(Cu1-yZny)3O7-delta compounds
over a wide range of composition (x, y, and delta). p was determined from the
room-temperature thermopower, S[290K]. When annealed at a given temperature and
oxygen partial pressure, a small but systematic variation in S[290K] was
observed with Zn, for all the samples. From the analysis of the temperature
derivative of resistivity, drho/dT, at 300K, which varies almost linearly with
p, irrespective of the composition of the sample, and the thermo-gravimetric
analysis (TGA), we have found that annealing under identical conditions makes
the Zn-substituted compounds somewhat more oxygen deficient compared to the
Zn-free ones
Structural and electrical properties of c-axis oriented Y1-xCaxBa2(Cu1-yZny)3O7-delta thin films grown by pulsed laser deposition
Ca- and Zn-subsituted Y1-xCaxBa2(Cu1-yZny)O7-delta (x = 0, 0.05 and y = 0,
0.02, 0.04, 0.05) thin films were grown on SrTiO3 (100) substrates using the
pulsed laser deposition (PLD) technique. Effects of various growth parameters
on the quality of the film were studied via X-ray diffraction (XRD), atomic
force microscopy (AFM), and in-plane resistivity, rhoab(T), measurements. The
deposition temperature and oxygen partial pressure were gradually increased to
820C and 1.20 mbar respectively. Films grown under these conditions exhibited
good c-axis orientation (primarily limited by the grain size) and low values of
the extrapolated residual resistivity, rho(0), at zero temperature. The planar
hole content, p, was determined from the room temperature thermopower, S[290K],
measurements and the effects of oxygen annealing were also studied. Fully
oxygenated samples were found to be overdoped with p ~ 0.195. The
Superconducting transition temperature Tc(p), and rho(T,p) showed the expected
systematic variations with changing Zn content.Comment: Submitted to Physica C (2003
The Doping Phase Diagram of Y1-xcaxba2(Cu1-yzny)3O7-d from Transport Measurements: Tracking the Pseudogap Below Tc (y = 0)
The effects of planar hole concentration, p, on the resistivity, r(T), of
sintered Y1-xCaxBa2(Cu1-yZny)3O7-d samples were investigated over a wide range
of Ca, Zn, and oxygen contents. Zn was used to suppress superconductivity and
this enabled us to extract the characteristic pseudogap temperature, T*(p),
from r(T,p) data below Tco(p) [ = Tc (y = 0)]. We have also located the
characteristic temperature, Tscf, marking the onset of significant
superconducting fluctuations above Tc, from the analysis of r(T,H,p) and r(T,p)
data. This enabled us to identify T*(p) near the optimum doping level where the
values of T*(p) and Tscf(p) are very close and hard to distinguish. We again
found that T*(p) depends only on the hole concentration p, and not on the level
of disorder associated with Zn or Ca substitutions. We conclude that (i) T*(p)
(and therefore, the pseudogap) persists below Tco(p) on the overdoped side and
does not merge with the Tco(p) line and (ii) T*(p), and thus the pseudogap
energy, extrapolates to zero at the doping p = 0.19 +/- 0.01.
PACS numbers: 74.25.Dw, 74.25. 74.62.Dh, 74.72.-h Key words: Pseudoap,
Superconducting fluctuationsComment: 14 pages (Text), 7 figure