Macroscopic Klein Tunneling in spin-orbit coupled Bose-Einstein   Condensates
  We propose an experimental scheme to detect macroscopic Klein tunneling with spin-orbit coupled Bose-Einstein condensates (BECs). We show that a nonlinear Dirac equation with tunable parameters can be realized with such BECs. %in a simple configuration to generate the artificial spin-orbit coupling. Through numerical calculations, we demonstrate that macroscopic Klein tunneling can be clearly detected under realistic conditions. Macroscopic quantum coherence in such relativistic tunneling is clarified and a BEC with a negative energy is shown to be able to transmit transparently through a wide Gaussian potential barrier. 
Dan-Wei Zhang, Zheng-Yuan Xue, Hui Yan, Z. D. Wang, and Shi-Liang Zhu
cond-mat.quant-gas quant-ph