where EF is the Fermi energy measured from the bottom of the Shockley state (i.e. the kinetic energy of the electrons in such a state), kF = √ 2EF m * is the associated Fermi wavevector, m * is the effective mass of the considered band and δF is the standard Fermi-level phase shift. They derived the above equation in the following way: for an interference-related density of states (DOS) difference, we obtain