Broken one-particle symmetry in few-electron coupled quantum dots

Few-electron systems confined in vertically coupled quantum dots are studied by exact methods and through the local spin density approximation (LSDA). Special attention is paid to the recovering of the one-particle symmetry properties in the LSDA. It is shown that—in spite of accurate energy estimates—the LSDA does not reproduce the one-particle parity and the relative probability of finding a definite number of electrons in the different quantum dots. This symmetry breaking appears for certain electron configurations and intermediate thickness of the interdot barrier and is a direct result of electron-electron correlation. We discuss the effect of correlation on the symmetry properties of the few-electron wave function and determine the limits of the applicability of the LSDA for coupled quantum dots.