K. Karpinska

Magnetotransport in the normal state of La 1.85 Sr 0.15 Cu 1 − y Zn y O 4 films

We have studied the magnetotransport properties in the normal state for a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y, between 0 and 0.12. A variable degree of compressive or tensile strain results from the lattice mismatch between the substrate and the film, and affects the transport properties differently from the influence of the zinc impurities. In particular, the orbital magnetoresistance (OMR) varies with y but is strain-independent. The relations for the resistivity and the Hall angle and the proportionality between the OMR and tan^2 theta are followed about 70 K. We have been able to separate the strain and impurity effects by rewriting the above relations, where each term is strain-independent and depends on y only. We also find that changes in the lattice constants give rise to closely the same fractional changes in other terms of the equation.The OMR is more strongly supressed by the addition of impurities than tan^2 theta. We conclude that the relaxation ratethat governs Hall effect is not the same as for the magnetoresistance. We also suggest a correspondence between the transport properties and the opening of the pseudogap at a temperature which changes when the La-sr ratio changes, but does not change with the addition of the zinc impurities.

Resistive and structural properties of La1.85Sr0.15Cu1−yZnyO4 films

Single-phase c-axis aligned La1.85Sr0.15Cu1−yZnyO4 films were grown by pulsed laser deposition with Zn contents up to a value of y of 0.12. The film properties indicate the existence of defects, in addition to the Zn impurities, that are unintentionally introduced during the film growth. These defects are probably oxygen vacancies, and have a distinctly different effect on Tc from the Zn. The separation of the two effects resolves earlier ambiguities in the observed rates of Tc depression.

Magnetic-field-induced localization in the normal state of superconducting La2-xSrxCuO4

Magnetoresistance measurements of highly underdoped superconducting La{sub 2{minus}x}Sr {sub x}CuO{sub 4} films with x=0.051 and x=0.048 , performed in dc magnetic fields up to 20T and at temperatures down to 40mK, reveal a magnetic-field{endash}induced transition from weak to strong localization in the normal state. The normal-state conductances per CuO{sub 2} plane, measured at different fields in a single specimen, are found to collapse to one curve with the use of a single scaling parameter that is inversely proportional to the localization length. The scaling parameter extrapolates to zero near zero field and possibly at a finite field, suggesting that in the zero-field limit the electronic states may be extended. {copyright} {ital 1997} {ital The American Physical Society}

Impurity and strain effects on the magnetotransport of La1.85Sr0.15Cu1-yZnyO4 films

The influence of zinc doping and strain related effects on the normal state transport properties(the resistivity, the Hall angle and the orbital magneto- resistance(OMR) is studied in a series of La1.85Sr0.15Cu(1-y)Zn(y)O4 films with values of y between 0 and 0.12 and various degrees of strain induced by the mismatch between the films and the substrate. The zinc doping affects only the constant term in the temperature dependence of cotangent theta but the strain affects both the slope and the constant term, while their ratio remains constant.OMR is decreased by zinc doping but is unaffected by strain. The ratio delta rho/(rho*tan^2 theta) is T-independent but decreases with impurity doping. These results put strong constraints on theories of the normal state of high- temperature superconductors.