Spin Sensitive Temperature Dependence of the Landau Levels in the Quantum Hall Regime

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Temperature dependence of the transition region between the quantum Hall plateaus has been measured at temperature between 50 mK and 1.8 K using a high mobility(110 mィイD12ィエD1/Vs) and two low mobility (〜18 mィイD12ィエD1/Vs) GaAs/AlGaAs hetero samples. V-shaped magnetic field distribution was produced by placing a single crystal platelet of a high Tc super conductor. We have found spin dependent temperature dependence of the spin split Landau levels. Landau levels with spin down have shown a shift of the transition region to the higher magnetic field when the temperature was increased during the field up process. Landau levels with spin up, on the other hand, have shown the temperature dependence as same as the normal sample, I.e., no effect of the magnetic field distribution was found. We have found these spin dependent temperature dependence occurs in the Landau levels with different Landau quantum number and both in samples with high and low mobility sample and, hence, the phenomenon is quite general. Further, when the magnetic field distribution was reversed by decreasing the magnetic field, spin dependence of the temperature dependence was symmetrically interchanged, I.e., Landau levels with spin up have shown a shift of the transition region to the lower magnetic field when the temperature was increased. There is no theory to explain these phenomena at present.