Fluctuations, size effects, and superconductivity in the CuO2 bilayer

Abstract

Recently, several experimental groups have found superconducting behavior of one-unit-cell (i.e., one CuO2 bilayer) thick YBa2Cu3O7 films. Using the functional-integral method, we calculate the critical temperature Tc for a system of two CuO2 planes coupled via a tunneling matrix element that results in Josephson-type coupling. The Coulomb interaction between the two planes is considered via inclusion of quantum phase fluctuations. We take into account the fluctuations of the modulus of the superconducting order parameter in the planes and the fluctuations of the phase difference of the order parameter between the planes. While for samples of infinite size Tc is strictly zero, samples of finite size L yield an effective two-dimensional to zero-dimensional transition at a finite temperature Tc*, characterized by a jump in the specific heat. We obtain Tc* as a function of L, Josephson coupling parameter, and Coulomb interaction strength and predict the temperature dependence of the specific heat near Tc*. Our results are consistent with the Tc* values observed on the single CuO2 bilayer.

Source-reported materials — not catalogue approval

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