Small exotic Stein manifolds.

link: http://arxiv.org/abs/0807.3815
Abstract

It is known that the only Stein filling of the standard contact structure on
S^3 is B^4. In this paper, we construct simply connected exotic compact Stein
4-manifold pairs for any Betti number $b_2 \geq 1$; we do this by enlarging
corks and plugs.