The Stiffnessometer - a magnetic-field-free superconducting stiffness meter and the nature of the phase transition in cuprates

The Stiffnessometer - a magnetic-field-free superconducting stiffness meter and the nature of the phase transition in cuprates

A new method to measure the superconducting stiffness tensor s, without subjecting the sample to magnetic field, is presented and applied to La1.875Sr0.125CuO4 (LSCO). The method is based on the London equation J=-sA, where J is the current density and A is the vector potential. Using rotor free A and measuring J via the magnetic moment of superconducting rings, we extract s. The technique, named Stiffnessometer, is sensitive to very small stiffness, which translates to penetration depth on the order of a few millimeters. We apply this method to two different LSCO 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. The Stiffnessometer results are accompanied by Low Energy SR measurements on the same sample to determine the stiffness anisotropy at favorable temperatures.