  Three-terminal devices with conduction channels formed by quasi-metallic
carbon nanotubes (CNT) are shown to operate as nanotube-based field-effect
transistors under strong magnetic fields. The off-state conductance of the
devices varies exponentially with the magnetic flux intensity. We extract the
quasi-metallic CNT chirality as well as the characteristics of the Schottky
barriers formed at the metal-nanotube contacts from temperature-dependent
magnetoconductance measurements.
