Anomalous Suppression of Valley Splittings in Lead Salt Nanocrystals   without Inversion Center
  Atomistic sp3d5s* tight-binding theory of PbSe and PbS nanocrystals is developed. It is demonstrated, that the valley splittings of confined electrons and holes strongly and peculiarly depend on the geometry of a nanocrystal. When the nanocrystal lacks a microscopic center of inversion and has T_d symmetry, the splitting is strongly suppressed as compared to the more symmetric nanocrystals with O_h symmetry, having an inversion center. 
A. N. Poddubny, M. O. Nestoklon, S. V. Goupalov
cond-mat.mes-hall