Resonances in quantum-dot transport

Scattering resonances in ballistic conduction across a quantum dot in a weak magnetic field are investigated. Due to the special geometry considered, the resonances grow narrower with decreasing B, until at B=0 they become bound states in the continuum. Whereas previously treated geometries exhibit at most one bound state with energy in the continuum, the number of such states in the present case is limited only by the number of transverse modes that the wire leads can sustain. Furthermore, the present model demonstrates the possibility of quantum-mechanical bound states in the continuum having a classical analog. The energy shifts of the resonances in a magnetic field show paramagnetic as well as diamagnetic behavior, which can be understood in terms of the dominant influence of a particular subband and its distance from the cutoff threshold in the dot region.