%0 Journal Article %T Instability of graphical strips and a positive answer to the Bernstein problem in the Heisenberg group %A D. Danielli %A N. Garofalo %A D. M. Nhieu %A S. D. Pauls %J Mathematics %D 2006 %I arXiv %X Let S be a C^2 H-minimal noncharacteristic hypersurface in the first Heisenberg group. We show that if S contains a graphical strip, then it is not a stable minimal surface. Moreover, we show that if S is a C^2 H-minimal noncharacteristic entire graph which is not itself a vertical plane, then S contains a graphical strip. Thus, as a corollary, we obtain an analogue of the Bernstein theorem: the only stable C^2 H-minimal noncharacteristic entire graphs are the vertical planes. %U http://arxiv.org/abs/math/0608516v1