Low-lyingstatesofaverticallycoupledthree-layerquantum-dotsystemarestudied.Eachlayercontainsoneelectron,andthetunnellingofelectronsbetweenlayersisneglected.EffectsoftheinterlayerseparationdandtheexternalmagneticfieldBareevaluatedbynumericalcalculations.Inthestrongcouplingcase(i.e.dissmall),asinasingledot,transitionsoftheangularmomentumLofthetruegroundstatesoccurwhenBincreases,whereasintheweakcouplingcasethetransitiondoesnotoccurandLremainszero.Furthermore,itisfoundthatthevariationofdmayalsoinducetheLtransition.Asaresult,aphasediagramofLofthetruegroundstateisgiveninthed-Bplane.
