Ellipsoidal deformation of vertical quantum dots

Addition energy spectra at 0 T of circular and ellipsoidally deformed few-e lectron vertical quantum dots ore measured and compared to results of model calculations within spin-density-functional theory. Because of the rotatio nal symmetry of the lateral harmonic confining potential, circular dots sho w a pronounced shell structure. With the lifting of the single-particle lev el degeneracies, even a small deformation is found to radically alter the s hell structure leading to significant modifications in the addition energy spectra. Breaking the circular symmetry with deformation also induces chang es in the total spin. This "piezomagnetic" behavior of quantum dots is disc ussed, and the addition energies for a set of realistic deformation paramet ers an provided. Far the case of the four-electron ground state at 0 T, a s pin-triplet to spin-singlet transition is predicted, i.e., Hund's first rul e no longer applies. Application of a magnetic held parallel to the current confirms that this is the case, and also suggests that the anisotropy of a n elliptical dot, in practice, may be higher than that suggested by the geo metry of the device mesa in which the dot is located. [S0163-1829(99)05839- 7].