Magnetic field enhancement of Coulomb blockade conductance oscillations in metal-metal oxide double barrier tunnel devices fabricated using atomic force microscope nanolithography
Abstract
Magnetic field enhancement of Coulomb blockade conductance oscillations in
metal oxide double barrier tunnel devices fabricated using atomic force microscope
nanolithography is reported for the first time. Anodic oxidation by this method was
accomplished on lithographically patterned Ti and Ni device layers. This is the first time
Ni has been reported to be oxidized via scanning probe lithography. Magnetoresistance
measurements were taken on selected devices in a Hall effect cryogenic system where
tunneling conductance behavior was observed at 1.8, 10, 25, and 50 K in the Ti devices
and 150 K in the Ni devices. Coulomb blockade conductance features were observed at
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1.8, 10 and 50 K in the Ti devices and 10 and 25 K in the Ni devices. Applying a 9T
magnetic field enhanced the conductance oscillations and clarified the Coulomb staircase
apparent in the I-V curves for both devices. From theoretical fits of the experimental
conductance behavior for the Ti devices, this is attributed to a suppression of cotunneling
currents in the device. Additionally, in multiple Ti devices, a zero-bias anomaly peak
was observed at ~ 2 K and is attributed to contaminant particles in the metal oxide barrier
creating a localized magnetic moment in the junction leading to spin-flip and s-d
exchange scattering assisted tunneling according to the Anderson-Appelbaum model.
This is the first time these zero-bias anomalies have been observed and reported in planar
tunnel junctions.
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