EFFECTS OF AN IMPURITY ON THE CONDUCTANCE AND THERMOPOWER OF A SADDLE-POINT-POTENTIAL QUANTUM POINT-CONTACT

The conductance G and the thermopower S of a saddle-point-potential qu antum point contact in the presence of a delta-potential impurity are calculated. For the case when an attractive impurity is located inside the quantum point contact, there are dips, peaks, and kinks in G. The se structures can be found below and near the band bottom of some tran sverse subbands, respectively. The peaks in G give rise to double peak s in S and the dips in G give rise to a shift in the peak positions of S, towards a smaller chemical potential value. In addition, a broad d ip in G is found to give rise to negative thermopower in regions betwe en the peaks of S. For the case when an attractive impurity is located in the classical forbidden region. for the electrons, we find in G th e structures that correspond to resonance tunneling and resonance refl ection. The corresponding S is found to show large and negative spikes . Our study shows that structures not so transparent in G manifest une quivocally in S, rendering S a very informative physical quantity to b e measured.