Fractional Quantum Hall Eect in a Diluted Magnetic Semiconductor

C. BETTHAUSEN; P. GIUDICI; B. PIOT

Wrocklav

Conferencia; EP2DS-2013; 2013

Here we report on the observation of FQH states in the lowest Landau level (LL) ofa 2DEG formed in two high quality 30nm wide Cd1-xMnxTe quantum wells with 0.24%and 0.30% of Mn concentration and densities of ns = 3:951011=cm2 and 2:771011=cm2,respectively. Standard magnetotransport experiments were performed up to 34T in atilted magnetic field and at temperatures between 15mK and 1 K. Due to the presence ofMn impurities the Zeeman energy is extremely high at low magnetic fields and is reducedwhen increasing the external field. We have designed our sample by adjusting the Mnconcentration such that the Zeeman splitting vanishes at about 13.5 T. This gave us theunique opportunity to investigate spin eects in QH states emerging at these elds. Bymeasuring activation energies at tilted magnetic fields we obtained the dependence onZeeman energy of the excitation gaps at filling factors nu = 4/3, 5/3, 7/5 and 8/5. Byanalyzing the excitation gap as a function of an in-plane magnetic field we demonstratethat exchange interaction between the Mn spins and the electrons crucially affects theproperties, e.g., the spin polarization, of FQH ground states. This provides a recipe totune the spin-splitting and hence the spin-polarization in a wide range, thus offering anovel means to manipulate fractional states. Using a simple model within the framework ofComposite Fermions (CFs) we extracted CF masses mCF and g-factors in the vicinity ofnu = 3/2. A quantitative comparison between model and experiment considering deviationscoming from disorder effects or LL broadening will be discussed.