The nature of the phase transition in La1.875Sr0.125CuO4 as determined by the Stiffnessometer - a magnetic-field-free superconducting stiffness meter

A new method to measure the superconducting stiffness tensor , without subjecting the sample to magnetic field, is applied to La_1.875Sr_0.125CuO₄ (LSCO). The method is based on the London equation , where  is the current density and  is the vector potential. Using rotor free  and measuring  via the magnetic moment of superconducting rings, we extract . 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 mSR measurements on the same sample to determine the stiffness anisotropy at favorable temperatures.