S. H. Naqib

Temperature dependence of electrical resistivity of high-Tc cuprates––from pseudogap to overdoped regions

Abstract The effects of planar hole concentration, p , and in-plane disorder, Zn ( y ), on the DC resistivity, ρ ( T ), of sintered samples of Y 1− x Ca x Ba 2 (Cu 1− y Zn y ) 3 O 7− δ were investigated over a wide doping range by changing both the oxygen deficiency ( δ ) and Ca content ( x ). From the ρ ( T , p ) data we extracted characteristic crossover temperatures on the underdoped and overdoped sides, T * and T m respectively, above which ρ ( T ) is linear. We compare our results with a number of other polycrystalline, thin film and single crystal cuprate superconductors and find similar behavior in the p -dependence of T * ( p ), T m ( p ), and the resistivity exponent, m ( p ), in fits to ρ ( T )= ρ 0 + aT m on the overdoped side. Our findings suggest that the doping level p =0.19±0.01 is special and could possibly be a quantum critical point in the sense that a transition between two different states takes place at zero temperature at this doping ( p crit ).

Doping phase diagram of Y1-xCaxBa2(Cu1-yZny)3O7-δ from transport measurements : Tracking the pseudogap below Tc

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 fluctuations

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, Χ(T), of La 2-x Sr x Cu 1-y Zn y O 4 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 La 2-x Sr x Cu 1-y Zn y O 4 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.