ArXiv · 2026
We investigate the interplay of in-plane magnetic and transverse electric fields in AB-stacked bilayer graphene. In prior work neglecting trigonal warping, we demonstrated that this configuration induces an insulator-metal transition purely via orbital effects, albeit requiring impractically large magnetic fields (>100 T). Here, we extend the analysis to the ultra-low-energy regime by incorporating interlayer skew couplings. In a restricted region of momentum space, trigonal warping produces a fine splitting of Dirac cones leading to a compensated semimetallic state at zero external field. Application of a transverse electric field above a small threshold (V_c∼0.6 meV) reinstates an insulating gap. When an in-plane magnetic field is applied, the orbital gauge vector immediately breaks the C₃ spatial symmetry of the lattice, and we uncover two sequential, field-driven transitions separated by an order of magnitude in scale. First, at fields (B ≈ 1 T), the Zeeman effect drives an indirect insulator-to-semimetal transition at the ungated charge neutrality point; the cross-spin gap closes, generating distinct electron and hole pockets separated in momentum space. Second, as the field increases to B ≈ 10--25 T, the orbital coupling closes the same-spin gap at an energy well away from the charge-neutral Fermi level. By electrostatically tuning the Fermi level to this specific gap-closing energy, we reveal the emergence of C₃-broken same-spin Fermi pockets, accompanied by a distinct step-like onset in the density of states. This dual-transition regime provides a highly sensitive platform for tunable, spin-selective transport.
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