Phase coherence and size effects in double quantum well mesoscopic wires

Conductance fluctuations (CF) have been observed when an in-plane magnetic field is applied to 800 nm-wide mesoscopic wires fabricated from GaAs/(AlGa)As double quantum well structures. This shows that the inter-well tunnelling transition preserves electron phase coherence. The CF disappear when the magnetic field becomes large enough to suppress tunnelling between the quantum wells. The CF amplitude is smaller when the tunnelling rate is reduced either by unbalancing the double well potential, or by increasing the thickness of the tunnel barriers. The wires display a strong magnetoresistance feature as the wells are decoupled by the in-plane magnetic field. This has been seen in macroscopic Hall bars, but is modified due to diffuse edge scattering in the wires.