To investigate the interaction of a crystalline lattice with high-temperature superconductivity as well as with magnetic flux lines, we measured temperature dependence of elastic constants and ultrasonic attenuation in single-crystalline La1.86Sr0.14CuO4 in magnetic fields of 0-14 T. In zero field, the elastic response to the superconducting transition was found to be remarkably anisotropic. The elastic constant C33 shows abrupt softening just below Tc. In contrast, C11 revealed no abrupt softening but change in the slope of temperature dependence. In magnetic field, elastic constants exhibit either an additional hardening due to the stiffness of the flux line lattice or an apparent softening probably due to the depression of superconductivity.
