  Armchair biphenylene nanoribbons are investigated by using density functional
theory. The nanoribbon that contains one biphenylene subunit in a unit cell is
a semiconductor with a direct band gap larger than 1 eV, while that containing
four biphenylene subunits is a metal. The semiconducting nanoribbon has high
electron mobility of 57174 cm2V-1s-1, superior to armchair graphene
nanoribbons. Negative differential resistance behavior is observed in two
electronic devices composed of the semiconducting and metallic nanoribbons. The
on/off ratios are in the order of 10^3. All these indicate that armchair
biphenylene nanoribbons are potential candidates for ultra-small logic devices.
