  We study a two-species Bose-Einstein condensates confined in
quasi-two-dimensional (quasi-2D) optical lattices at finite temperatures,
employing the Hartree-Fock-Bogoliubov theory with the Popov approximation. We
examine the role of thermal fluctuations on the ground-state density
distributions, and the quasiparticle mode evolution. At zero temperature, the
geometry of the ground-state in the immiscible domain is side-by-side. Our
results show that the thermal fluctuations enhance the miscibility of the
condensates, and at a characteristic temperature the system becomes miscible
with rotationally symmetric overlapping density profiles. This
immiscible-miscible transition is accompanied by a discontinuity in the
excitation spectrum, and the low-lying quasiparticle modes such as slosh mode
becomes degenerate at the characteristic temperature.
