Abstract
A method to measure the superconducting (SC) stiffness tensor bar rho _{mathrm{s}}, without subjecting the sample to external magnetic field, is applied to La1.875Sr0.125CuO4. The method is based on the London equation {mathbf{J}} = - {bar{mathbf{rho }}}_{mathrm{s}}{mathbf{A}}, where J is the current density and A is the vector potential which is applied in the SC state. Using rotor free A and measuring J via the magnetic moment of superconducting rings, bar rho _{mathrm{s}} at T → Tc is extracted. The technique is sensitive to very small stiffnesses (penetration depths on the order of a few millimeters). The method is applied to two different rings: one with the current running only in the CuO2 planes, and another where the current must cross planes. We find different transition temperatures for the two rings, namely, there is a temperature range with two-dimensional stiffness. Additional low energy muon spin rotation measurements on the same sample determine the stiffness anisotropy at T < Tc.
Highlights
A method to measure the superconducting (SC) stiffness tensor ρs, without subjecting the sample to external magnetic field, is applied to La1.875Sr0.125CuO4
The magnetization measurements were done in both c-needles, where the CuO2 planes are perpendicular to the field direction, and a-needles where the planes are parallel to the field
We focus on the “anomalous doping” x = 1/8 regime, where the difference between the two transition temperatures is large, and minute inhomogeneity of Strontium doping does not lead to significant deviations in the transition temperatures. (Details of materials preparation are given in the Methods section.) Our major finding is that in LSCO x = 1/8 there is a temperature interval of 0.7 K where global 2D SC
Summary
A method to measure the superconducting (SC) stiffness tensor ρs, without subjecting the sample to external magnetic field, is applied to La1.875Sr0.125CuO4. Zero resistivity and diamagnetism do not require bulk superconductivity and can occur due to superconducting islands or filaments It is not clear whether the observed in-plane superconductivity is a macroscopic phenomenon and if the sample supports global 2D stiffness as expected from Kosterlitz– Thouless–Berezinskii (KTB) theory[9,10,11]. If it does, there should be a temperature (and doping) range where the intra-plane stiffness 1=λ2ab is finite, while the inter-plane stiffness 1=λ2c is zero (λ is the penetration depth).
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