Anomalous tunneling transparency of double-barrier quantum wells with transition-metal impurities

A mechanism for the anomalous transparency of a double-barrier quantum well (DBQW) doped with transition-metal impurity is proposed. Apart from the usual resonance peaks, strong features appear in the tunneling transparency, since such a DBQW possesses its own quasi-two-dimensional (2D) continuum together with the impurity level. These strong peaks arise near the edges of 2D bands due to the reconstruction of 2D continuum states in a process of tunneling via a doped DBQW. As a result, the tunneling transparency can have peaks even when the deep impurity level is out of resonance with the chemical potential. Unlike the well-known Kondo singularities, the impurity-induced resonances are temperature independent. The influence of Kondo scattering on these features is also considered.