Fig. 4.

Differential spin-injection (p _in) and detection (p _d) polarizations of the cobalt/bilayer-hBN/graphene contacts. a Differential spin-injection polarization p _in of four contacts with 2L-hBN tunnel barrier, as a function of the DC voltage bias V. Top axis represents the corresponding electric-field (=V/t _hBN, t _hBN ≈7 Å, the thickness of 2L-hBN barrier) induced across the Co/2L-hBN/graphene contacts. Note that the ΔR _nl used to calculate $p_{\mathrm{in}}^8$ in Fig. 3b is obtained from a different data set. b Differential spin-detection polarization p _d of contacts 8 and 9 as a function of DC voltage bias V applied across the detector, while the injector bias is fixed at I _in = + 20 μA. The insets in a and b show p _in and p _d of contacts at zero bias, respectively. The top x axis in a and b indicates the electric field corresponding to the applied bias across the contacts