Le jeudi 19  février 2009, 11h00

Sterling Garmon (LPTMC)

Due to recent advances in nano-technology, various ways to manufacture a one-dimensional semiconductor quantum wire have been developed.  It has been proposed that the bound states in continuum (BIC) phenomenon (first discovered theoretically by von Neumann and Wigner in 1929) might be experimentally observed in these devices.  I will present one theoretical realization of this effect, which occurs in a single quantum wire coupled with multiple adatom impurities.  I will also present the general conditions under which the BIC effect may occur; most importantly, the potential must contain a zero within the continuous energy spectrum.  I will also demonstrate a related phenomenon, which we term the quasi-bound state in continuum (QBIC).  I will show that this phenomenon may occur in a two-channel quantum wire (in which there are two overlapping energy bands) coupled with a single adatom.  I will again discuss the general conditions under which the QBIC effect occurs; most importantly, there must be overlapping energy bands and at least one van Hove singularity in the density of states at the edge of one of the bands.  The advantage to the QBIC effect is that the BIC states only occur at discrete points of parameter space (i.e., it is a measure zero effect), while the QBIC states occur over a wide range of parameter space and hence may be easier to detect experimentally.