  This work presents theoretical demonstration of Aharonov-Bohm (AB) effect in
monolayer phosphorene nanorings (PNR). Atomistic quantum transport simulations
of PNR are employed to investigate the impact of multiple modulation sources on
the sample conductance. In presence of a perpendicular magnetic field, we find
that the conductance of both armchair and zigzag PNR oscillate periodically in
a low-energy window as a manifestation of the AB effect. Our numerical results
have revealed a giant magnetoresistance (MR) in zigzag PNR (with a maximum
magnitude approaching two thousand percent). It is attributed to the AB effect
induced destructive interference phase in a wide energy range below the bottom
of the second subband. We also demonstrate that PNR conductance is highly
anisotropic, offering an additional way to modulate MR. The giant MR in PNR is
maintained at room temperature in the presence of thermal broadening effect.
