Signs of quantum dot-lead matrix elements: The effect on transport versus spectral properties

A small quantum dot coupled to two external leads is considered. Different signs of the dot-lead coupling matrix elements give rise to qualitatively different behavior of physical observables such as the conductance, the phase of the transmission amplitude, and the differential capacitance of the dot. For certain relative signs the conductance may vanish at values of the gate potential, where the spectral density is maximal. Zeroes of the conductance are robust against increasing the dot-lead coupling. They are associated with abrupt phase lapses in the transmission phase whose width vanishes as the square of the temperature. We carefully distinguish between phase lapses of -pi and phase antilapses of pi. ©2002 American Physical Society