Spontaneous strain in high-temperature superconductor La1.85Sr0.15CuO4

The lattice parameters of La1.85Sr0.15CuO4 were measured by an x-ray Rietveld method between 15 K and room temperature. A change in a lattice parameter could be detected at superconducting phase transition. It is pointed out, for the first time, that the change can be attributed to a spontaneous strain in the superconducting phase caused by coupling between a superconducting order parameter and the strain.