  Theoretical studies on spin-dependent transport through helical molecules
with straight spiral geometry have received intense research interest in the
past decade, however, the physics in circular helical molecules has still less
been explored. In this work, we theoretically construct a circular single helix
(CSH) possessing the chirality-induced spin-orbit coupling and contacting with
two non-magnetic electrodes. Our theoretical calculations demonstrate that the
spin-related transport in CSH exhibits the so-called chiral-induced spin
selectivity (CISS) effect and more importantly, the CISS-reduced spin-dependent
destructive quantum interference (DQI) also occurs in the CSH, without any
external magnetic field or magnetic electrodes. Moreover, the changing of CSH
length or the electrode positions exhibits specific patterns in the
spin-polarized conductance. Particularly, the dephasing magnitude can adjust
effectively these two spin-dependent effects to realize their coexistence.
Additionally, the phase transition between the CISS-dependent constructive
quantum interference (CQI) and DQI is also observed in the CSH. Our theoretical
work puts forwards a new material plateau to explore the CISS and to exhibit
the novel CISS-dependent CQI effect.
