correct sign in spin_potential_shape tutorial
For a spin-orbit term of the form '-iασ_y∂_x' the hopping for 'HoppingKind((1, 0), lat)' (from 'x' to 'x + a') is 'iασ_y'.
Closes #175 (closed).
For a spin-orbit term of the form '-iασ_y∂_x' the hopping for 'HoppingKind((1, 0), lat)' (from 'x' to 'x + a') is 'iασ_y'.
Closes #175 (closed).