Electron Channelling by Microscopic Magnetic Potentials
Nogaret, A., 2002. Electron Channelling by Microscopic Magnetic Potentials. Semimag-15 Proceedings
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While conventional electronic devices rely on electrostatic potentials to accelerate and confine charge carriers, a novel type of device has been proposed that uses inhomogeneous magnetic fields to channel and filter electrons. The stray fields emanating from ferromagnetic stripes fabricated at the surface of a two dimensional electron gas were used to deflect the ballistic electrons underneath. Magnetotransport experiments reveal a resistance resonance due to the formation of two types of magnetic edge states that drift in opposite directions perpendicular to the magnetic field gradient. A systematic study of Ni, Fe and Dy devices shows that the peak position increases proportionally to the amplitude of the magnetic modulation. The magnetic origin of the resonance is further evidenced by the collapse of channelling above the Curie temperature of dysprosium. Its helical/ferromagnetic phase transition provides an original means for switching on the magnetic modulation independently of the applied magnetic field by changing the temperature. We use this effect to demonstrate that the magnetoresistance due to snake orbits is one order of magnitude higher that the magnetoresistance due to the stripe being magnetised while the modulation remains uniformly positive. Experiments in tilted magnetic fields demonstrate that both the resonant peak and the ratio of the Hall resistance upon the Hall resistance of the bare 2D electron gas scale with the perpendicular component of the applied magnetic field. This demonstrates that the Hall resistance measures the trapping of electrons in or out of magnetic edge states rather than the average magnetic field in the Hall junction. Both results were expected from a simple drift-diffusion picture. Discrete resistance steps obtained when changing the electron density are tentatively assigned to the formation of quantum confined 1D snake subbands. The gate bias dependence of the resonant peak is discussed in relation to the realistic modulation profile.
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