Nature Communications 3: Article number: 982 (2012); Published: 31 July 2012; Updated: 21 May 2013.

In the Discussion section of this Article, we incorrectly claimed that an in-plane magnetic field will generate Dirac mass terms for the surface states. Instead, the in-plane magnetic field merely shifts the location of the Dirac points. The k·p Hamiltonian in the presence of an in-plane field (B1, B2) (in the local basis defined in the Article) is

where μB is the Bohr magneton and g1,2 is the g-factor of Dirac surface states.