Direct observation of a structural-fluctuation enhancement in a superconducting state of ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ by electron diffraction

Features of temperature-dependent diffuse scattering showing a structural fluctuation in ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{10}$ have been investigated in detail in a temperature range between about 20 K and room temperature by means of electron diffraction. As the temperature is lowered, the intensity of diffuse scattering increases remarkably below about 130 K, which is taken to be the onset temperature of superconductivity. Because the scattering is obviously due to a structural fluctuation, ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{10}$ is understood to exhibit an enhancement of the fluctuation in a superconducting state. In addition, a careful analysis of the features in the scattering suggests that a dynamic displacement of an apical O atom in the ${\mathrm{CuO}}_5$ pyramid along the c axis is responsible for the structural fluctuation in the superconducting state.