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Pulsed laser deposition was used to grow c-axis aligned films of La2−xSrxCuO4−δ, with Sr content, x, in the range of 0.03 to 0.2, on substrates prepared from single-crystalline SrLaAlO4, with a lattice mismatch of 0.5%. The thickness dependence of Tc0, the temperature at which the resistance falls to zero, is much reduced compared to that of films deposited on SrTiO3, where the lattice mismatch is 3.4%. The maximum Tc0 is achieved at x=0.15 for both types of substrates. While the thickness dependence is related to the strain resulting from the lattice mismatch, the value of the maximum Tc0 is determined by the oxygen concentration.

Single-crystalline films of La2−xSrxCuO4 have been grown epitaxially on SrTiO3, NdGaO3, and LaSrAlO4 substrates by laser ablation. We show that record values of the superconducting transition temperature may be achieved by high-pressure annealing in oxygen. The films exhibit values of Tco above 38 K, as well as a linear variation of the resistivity with T and excellent crystal quality.

The normal-state Hall coefficient RH and the in-plane resistivity ρ ab are measured in La-doped Bi2Sr2CuOy (Tc ≃ 13 K) single crystals and La2−xSrxCuO4 thin films by suppressing superconductivity with 61-T pulsed magnetic fields. In contrast to data above Tc, the RH below ∼ 10 K shows little temperature dependence in all the samples measured, irrespective of whether ρ ab exhibits insulating or metallic behavior. Thus, whatever physical mechanism gives rise to insulating behavior in the low-temperature normal state, it leaves the Hall conductivity relatively unchanged.PACS numbers: 74.25.Fy, 74.20.Mn, 74.72.Hs, 71.10.Hf Application of a pulsed high magnetic field to suppress superconductivity in the high-T c cuprates has opened up the possibility for measurements of normal-state transport at low temperatures. This regime has been rather unexplored due to the extremely high H c2 of the cuprates. Thus far the anisotropic normal-state resistivity has been measured in La 2−x Sr x CuO 4 (LSCO) [1,2] and La-doped Bi 2 Sr 2 CuO y (Bi-2201) [3] down to subkelvin temperatures using 61-T pulsed magnetic fields.One of the surprising findings in the low-temperature normal-state resistivity of LSCO is an unusual log(1/T ) divergence of both in-plane (ρ ab ) and c-axis resistivity (ρ c ) of underdoped samples. Similar divergence of resistivity that is consistent with log(1/T ) is also found in disordered Bi-2201 [3], where the dynamic range of the divergence is generally smaller than in underdoped LSCO, where the increase of ρ ab can be as large as a factor of three. Although the origin of the unusual log(1/T ) behavior is not yet clear, there are several proposed explanations, some of which involve the localization of the charge-carrying quasi-particles [4,5], others of which involve the suppression of the two-dimensional density of states near the Fermi energy. In this latter scenario, the low-temperature insulating behavior in the cuprates might result from conventional disorder-enhanced electron interactions [6], from the temperature-dependent impurity scattering time in the marginal Fermi liquid [7], or from the existence of a pseudo-gap in the underdoped high-T c cuprates [8].In conventional physics of disordered metals in twodimensions, both weak localization and electron-electron interactions give rise to identical log(1/T ) corrections to the resistivity. Measurement of the Hall coefficient R H is useful in separating these two physical mechanisms [6]: weak localization does not affect R H , while interactions lead to corrections in R H which are two times larger than the corrections to the resistivity. The physics of the cuprates is expected to be very different from that of conventional disordered metals. Indeed, three independent reports of logarithmic behavior in underdoped cuprates provide three separate arguments against interpretations involving conventional weak localization [1,9,10]. Nevertheless, measurement of the Hall effect down to low temperatures could help resolve which of the proposed physical mech...