# Chiral tunnelling in graphene

I am trying to reproduce the results of this paper: Chiral tunnelling in single and bilayer graphene.

I have done all the math but I couldn't figure out how the $$s(=sgn(E))$$ and $$s'(=sgn(E-V_0))$$ terms are coming in the second component of the wave function ,i.e., in $$\psi_2(x, y)$$.

I know I am missing something trivial. Please someone point that out to me. Thanks.