Period Halving of Persistent Currents in mesoscopic Mobius Ladders

We investigate the period halving of persistent currents (PCs) of non-interacting electrons in isolated mesoscopic Mobius ladders without disorder,pierced by Aharonov-Bohm flux.The mechanisms of the period halving effect depend on the parity of the number of electrons as well as on the interchain hopping.Although the data of PCs in mesoscopic systems are sample specific,some simple rules are found in the canonical ensemble average,for example,all the odd harmonics of the PCs disappear and the signals of even harmonics are non-negative.