Various phase transitions in = 2 bilayer quantum Hall states

AbstractWe measured the magnetoresistance in bilayer quantum Hall (QH) state at fractional lling factor = 23 . Surprisingly,for dierent QH areas and two types of hysteresis were observed by controlling the total electron density and the densitydierenceintwolayers.TwoQHareasandonetypeofhysteresisarenovelcharacteristicofbilayersystems. ? 2002ElsevierScienceB.V.Allrightsreserved. PACS:73.43.Np;73.43.Qt;73.40.KpKeywords:FractionalquantumHalleect;GaAs =AlGaAs;Bilayer system; Composite fermion ThebilayerquantumHall(QH)statehasattractedagreatdealofrecentattention,wherethestructurein-troducesadditionaldegreesoffreedominthethird(z)direction. In this system, spin-split Landau levels(LLs) further split in the bonding and antibondingstates of electron wave functions localized in eachlayer. It is convenient to use pseudospin language,wherepseudospinP z = 12 (P z = − 12 )referstoanelec-troninthefront(back)layer.Atthellingfactor =2,the competition between the pseudospin-Zeeman ef-fectandtheZeemaneectleadstoaphasetransitionbetween the spin-polarized and the spin-unpolarizedstates [1–5]. However, only a few researches havebeen done at bilayer fractional QH eects [6]. The2=