correction: in figure 2a of this letter, the resistance for the right-hand element of the bottom circuit should be r_off(1-w/d), instead of the shown value r_offw/d. also, the correct value of window function should be w(d-w)/d², rather than w(1-w)/d². all simulation results presented in the paper use the correct formulae.correction: in figure 2a of this letter, the resistance for the right-hand element of the bottom circuit should be r_off(1-w/d), instead of the shown value r_offw/d. also, the correct value of window function should be w(d-w)/d², rather than w(1-w)/d². all simulation results presented in the paper use the correct formulae.