  Parity-time (PT) symmetry is of great interest. The reciprocal and
unidirectional features are intriguing besides the PT symmetry phase
transition. Recently, the reciprocal transmission, unidirectional
reflectionless and invisibility are intensively studied. Here, we show the
reciprocal reflection/transmission in PT -symmetric system is closely related
to the type of PT symmetry, that is, the axial (reflection) PT symmetry leads
to reciprocal reflection (transmission). The results are further elucidated by
studying the scattering of rhombic ring form coupled resonators with enclosed
synthetic magnetic flux. The nonreciprocal phase shift induced by the magnetic
flux and gain/loss break the parity (P) and time-reversal (T) symmetry but keep
the parity-time (PT) symmetry. The reciprocal reflection (transmission) and
unidirectional transmission (reflection) are found in the axial (reflection)
PT-symmetric ring center. The explorations of symmetry and asymmetry from PT
symmetry may shed light on novel one-way optical devices and application of PT
metamaterials.
