Abstract
In bilayer graphene, the phase diagram in the plane of a strain-induced bare nematic term and a top-bottom gates voltage imbalance is obtained by solving the gap equation in the random-phase approximation. At nonzero and , the phase diagram consists of two hybrid spin-valley symmetry-broken phases with both nontrivial nematic and mass-type order parameters. The corresponding phases are separated by a critical line of first- and second-order phase transitions at small and large values of , respectively. The existence of a critical end point where the line of first-order phase transitions terminates is predicted. For , a pure gapped state with a broken spin-valley symmetry is the ground state of the system. As increases, the nematic order parameter increases, and the gap weakens in the hybrid state. For , a quantum second-order phase transition from the hybrid state into a pure gapless nematic state occurs when the strain reaches a critical value. A nonzero suppresses the critical value of the strain. The relevance of these results to recent experiments is briefly discussed.
- Received 18 April 2012
DOI:https://doi.org/10.1103/PhysRevB.86.125439
©2012 American Physical Society