Quantum contextuality for a relativistic spin-1/2 particle
  The quantum predictions for a single nonrelativistic spin-1/2 particle can be reproduced by noncontextual hidden variables. Here we show that quantum contextuality for a relativistic electron moving in a Coulomb potential naturally emerges if relativistic effects are taken into account. The contextuality can be identified through the violation of noncontextuality inequalities. We also discuss quantum contextuality for the free Dirac electron as well as the relativistic Dirac oscillator. 
Jing-Ling Chen, Hong-Yi Su, Chunfeng Wu, Dong-Ling Deng, Adan Cabello,   L. C. Kwek, C. H. Oh
quant-ph