Complex-barrier tunnelling times

(Received 24 August 1994, receved in final form 9 September 1994, accepted 20 September 1994)

Abstract
In this paper we calculate the analytic expression of the phase time for the scattering of an electron off a complex square barrier. As is well known the (negative) imaginary part of the potential takes into account, phenomenologically, the absorption. We investigate the Hartman-Fletcher effect, and find that it is suppressed by the presence of a (non negligible) imaginary potential. In fact, when a suffficiently large absorption is present, the asymptotical transmission speed is finite. Actually, the tunnelling time does increase linearly with the barrier width. A recent optical experiment seems to be in agreement with our theoretical expectation.