O. Vanbesien et D. Lippens, DIRECTIONAL COUPLING IN DUAL-BRANCH ELECTRON-WAVE-GUIDE JUNCTIONS, Physical review. B, Condensed matter, 52(7), 1995, pp. 5144-5153
We present a detailed analysis of a quantum directional coupler. The i
nnovative aspect of the proposal comes from a dual coupling scheme. Wi
th respect to structures with a single interaction window, the crucial
advantage is that the phase in the output leads can be strongly modul
ated through the distinct coupling paths. As a consequence, the propos
ed structure is highly directional in a four-terminal configuration. I
n order to address the above idea, a theoretical analysis is conducted
by solving the two-dimensional Schrodinger equation using a mode-matc
hing technique. Transmission spectra and conductance variations are ca
lculated and interpreted paying attention to the influence of structur
al parameters such as wire widths and branch-line coupling lengths. On
this basis, a parametric analysis is carried out including notably st
udies of the multimode operation and of the influence of electrostatic
potential variations along the direction of propagation. Various mode
s of operation are pointed out. First, we illustrate a 3-dB coupling s
ituation with a directivity as high as 35 dB in the monomode limit whe
re the dearest interference effects are expected. Second, a real-space
transfer mechanism with over 90% of transferred electrons is proposed
as the operating mechanism of a quantum interference electronic switc
h. At last, the time response of mechanisms is discussed by viewing th
e transfer of electrons as a resonance process.