We propose here a model for the pair tunneling states observed by Ashoori and co-workers (Phys. Rev. Lett. {\bf 68}, 3088 (1992)) in GaAs quantum dots. We show that while GaAs is a weakly-polar semiconductor, coupling to optical phonons is sufficiently strong to mediate a negative-U pairing state. The physical potential in which the two electrons are bound can be composed of a Si impurity and a parabolic well that originates from the potential created by the δ−dopants in the backing layer of the dot. Such a pair state breaks up at moderate magnetic field strengths (≈ 2 T), as is seen experimentally, and is unstable when the confining radius of the dot is smaller than ≈400\AA.
@article{arxiv.cond-mat/9510017,
title = {Pair Tunneling in Semiconductor Quantum Dots},
author = {Yi Wan and Gerardo Ortiz and Philip Phillips},
journal= {arXiv preprint arXiv:cond-mat/9510017},
year = {2009}
}