Abstract
A possible occurrence of cooperative Jahn-Teller distortion in La2CuO4 is suggested. In doped (La1-xMx)2CuO4 the d holes in Cu2+ ions in |x2-y2> orbitals tend to form a polaron pair in the Cu2+-O2--Cu2+ form, and consequently extra d holes in |z2> orbitals in Cu3+ ions also form a polaron pair in a less distorted situation. Then the coherent tunneling of an extra bipolaron occurs through all the Cu2+-O2--Cu2+ sites, and the extra bipolarons make a Bose condensation at the zero wavevector state. This causes high Tc superconductivity. Tc is related to the superexchange between the spins of d holes in |z2> orbital and suggested not to exceed the Neel temperature of La2CuO4.