Abstract
We employ coupled parallel double quantum point contacts to study the quantum decoherence and the transport of spin-polarized currents in quantum wires. The devices are fabricated on the GaAs/Al0.3Ga0.7As heterostructures with two-dimensional electron gas. In the experiment, the structure of quantum wires are formed on the layer of two-dimensional electron gas by means of quantum point contacts, and the electrical transport measurements are done at ultra-low temperatures. We study the phase coherence in a quantum-wire system by quantum interference phenomena, and besides we utilize the conductance additivity in a pair of parallel quantum wires to study the interaction between the quantum wires. Firstly, we use the Aharonove-Bohm oscillation to see how quantum interference depends on the mode number in parallel double quantum wires. We find that the magnitude of the oscillation decreases with the decrease of the mode number, accompanying fluctuation. The decrease of the oscillation magnitude can be understood as the result of the decrease of transmission probability, and the fluctuation possibly relates to the phase coherence. Then, we investigate the temperature dependence of the Ramsauer-type resonance to study the quantum decoherence in a quantum-wire system. We find that the temperature dependence of the Ramsauer-type resonance can be explained and analyzed by thermal averaging effect, and the tendency of the temperature dependence does not vary with the mode number in the system. Finally, we use conductance additivity as a tool to study the interaction between the spin-polarized currents through the coupled parallel double quantum wires. The conductance additivity is valid at zero magnetic field. However, when the electrons are spin-polarized at a high magnetic field parallel to the two-dimensional electron gas, the additivity is failed, and extra quantum states are observed. The breakdown of the additivity and the emergence of the extra states possibly result from the interaction between the spin-polarized currents.