ELSPNIER 17 October 1994 Physics Letters A 193 (1994) 485-490 PHYSICS LETTERS A The effect of Coulomb blockade on resonant tunneling Hocine Bahlouli Physics Department,KingFahd University ofPetroleumand Minerals,Dhahran31261, SaudiArabia Received 18 June 1994; revised manuscript received 5 August 1994; accepted for publication 8 August 1994 Communicatedby L.J. Sham Abstract The current-voltage characteristic and conductance of a tunnel junction containing a single impurity localized state in the barrier region are studied using the kinetic equation approach. It is shown that the presence of the on-site Coulomb interaction, U, gives rise to a step in the conductance G(V) when the applied voltage becomes close to U. When averaging over U is taken into account, this step-like behavior is smoothed out over the maximum range of the potential distribution. Theoretical and experimental interest in transport via localized states in tunnel junctions is a subject of in- creasing interest due to its importance in microelectronic device applications [ 1 ]. At the same time it consti- tutes a fertile ground on which one can test the basics of quantum mechanics at the macroscopic level. When localized states are present in a tunnel barrier, current flow in the junction can arise from three possible processes. The first is the direct tunneling, in which the electron tunnels directly all the way across the barrier, usually the magnitude of this effect is exponentially small. The second is elastic resonant tunneling in which the electron in one lead tunnels first to a localized state (LS) in the barrier then from the LS to the other lead [2]. The third process is the indirect hopping via two LS in the bander separated in energy, this process is due to phonon absorption or emission. At low temperatures and small applied voltages, resonant tunneling through a single LS dominates the transport. Evidence for such a contribution was observed experimentally [ 3 ]. When we increase the bias voltage, the process of phonon assisted hopping via LS starts to dominate [ 4 ]. Experimental evidence for the contribution of such a hopping process to transport has also been supported by the recent experimental data [ 3 ]. In our present study we will restrict ourself to resonant tunneling and study the effect of the on-site Coulomb correlation on the conductance and current-voltage characteristic. The Hamiltonian describing our system is defined by + ~ (Tka'~oao+h.c.)+ ~ (Tpa+ao+h.c.), (I) where ek~ ak~ are the energy and annihilation operator for an electron in the left lead, similar quantities with subscript p refer to the right lead. The quantities e~, a° and no refer to the energy, annihilation operator and occupancy of the impurity state, respectively. In formula ( l ) h.c. stands for Hermitian conjugate. The parame- ter U represents the on-site Coulomb interaction while T, and Tp are the transition matrix elements from the 0375-9601/94/$07.00 © 1994 ElsevierScienceB.V. All rights reserved SSDI0375-9601 (94)00673-3