▎ 摘　　要

We show that bilayer graphene (BLG) exhibits magnetoelectric (ME) effects that are formally similar to those commonly seen in band insulators with broken inversion and time-reversal symmetries. Three unusual features characterize the ME responses exhibited by BLG: (i) unlike most other ME media, BLG is a conductor, (ii) BLG has a nonquantized ME coupling even though its electronic structure does not break parity and time-reversal symmetry, and (iii) the magnitude of the ME coupling in BLG is determined by the valley-isospin density, which can be manipulated experimentally. This last property also enables a purely electricmeasurement of valley-isospin densities. While our theoretical arguments use BLG as an example, they are generally valid for any material with similar symmetries.