Effects of signs in tunneling matrix elements on transmission zeros and phase

The effect of the signs in the tunneling matrix elements on the transmission zeros and the transmission phase in transport through a quantum dot is studied. The existence of transmission zeros is determined by both the relative signs and the strength of the tunneling matrix elements for two neighboring energy levels of a dot. The experimentally observed oscillating behavior of the transmission phase over several Coulomb peaks can be explained by a uniform distribution of the relative signs. Based on a simple model of a quantum dot, we present a possible scenario which can give such uniform signs over several conductance peaks. We suggest that the location of the transmission zeros can be identified by inspecting the Fano interference pattern in the linear response conductance of a closed Aharonov-Bohm (AB) interferometer with an embedded quantum dot as a function of the number of electrons in the dot and the AB flux.