简介：Byusingthecoupledclustermethodandthenumericaldensitymatrixrenormalizationgroupmethod,weinvestigatethepropertiesofthequantumplateaustateinanalternatingHeisenbergspinchain.Intheabsenceofamagneticfield,theresultsobtainedfromthecoupledclustermethodanddensitymatrixrenormalizationgroupmethodbothshowthatthegroundstateofthealternatingchainisagappeddimerizedstatewhentheparameterαexceedsacriticalpointαc.Thevalueofthecriticalpointscanbedeterminedpreciselybyadetailedinvestigationofthebehaviorofthespingap.Thesystemthereforepossessesanm=0plateaustateinthepresenceofamagneticfieldwhenα>αc.Inadditiontothem=0plateaustate,theresultsofdensitymatrixrenormalizationgroupindicatethatthereisanm=1/4plateaustatethatoccursbetweentwocriticalfieldsinthealternatingchainifα>1.Themechanismforthem=1/4plateaustateandthecriticalbehaviorofthemagnetizationasoneapproachesthisplateaustatearealsodiscussed.