Electric-field control of bound states and optical spectrum in window-coupled quantum waveguides

Abstract

The properties of the bound states of two quantum waveguides coupled via the window of the width s in their common boundary are calculated under the assumption that the transverse electric field E is applied to the structure. It is shown that the increase in the electric intensity brings closer to each other fundamental propagation thresholds of the opening and the arms. As a result, the ground state, which in the absence of the field exists at any nonzero s, exhibits the energy E0 decrease for the growing E and in the high-field regime E0 stays practically the same regardless of the size of the connecting region. It is predicted that the critical window widths scrn, n=1,2,…, at which new excited localized orbitals emerge, strongly depend on the transverse voltage; in particular, the field leads to the increase in scrn, and, for quite strong electric intensities, the critical width unrestrictedly diverges. This remarkable feature of the electric-field-induced switching of the bound states can be checked, for example, by the change of the optical properties of the structure when the gate voltage is applied; namely, both the oscillator strength and absorption spectrum exhibit a conspicuous maximum on their E dependence and turn to zero when the electric intensity reaches its critical value. Comparative analysis of the two-dimensional (2D) and 3D geometries reveals their qualitative similarity and quantitative differences.