Transport gap in suspended bilayer graphene at zero magnetic field

Abstract

We report a change of three orders of magnitude in the resistance of a suspended bilayer graphene flake which varies from a few k in the high-carrier-density regime to several M around the charge neutrality point (CNP). The corresponding transport gap is 8 meV at 0.3 K. The sequence of quantum Hall plateaus appearing at filling factor ν = 2 followed by ν = 1 suggests that the observed gap is caused by the symmetry breaking of the lowest Landau level. Investigation of the gap in a tilted magnetic fields indicates that the resistance at the CNP shows a weak linear decrease for increasing total magnetic field. Those observations are in agreement with a spontaneous valley splitting at zero magnetic field followed by splitting of the spins originating from different valleys with increasing magnetic field. Both the transport gap and B field response point toward the spin-polarized layer-antiferromagnetic state as the ground state in the bilayer graphene sample. The observed nontrivial dependence of the gap value on the normal component of B suggests possible exchange mechanisms in the system.

Chirald-wave superconductivity in doped graphene

“…Bilayer graphene Bilayer graphene has received a lot of attention, mainly because of the enhanced density of states at zero doping due to parabolically touching bands. Such band structures have been shown to be unstable towards spontaneous symmetry breaking [152] and experimental results have revealed signatures of interaction-driven excitonic states in suspended and undoped graphene bilayers [18,19,20,21,22,23,24,25]. Very recently weak-coupling renormalization group calculations have shown that superconductivity emerges upon doping away from these excitonic states [153].…”

“…[4,5,6,7,8,9,10,11,12,13,14,15,16,17], but most have not been experimentally observed as of yet. One exception is multi-layer graphene systems where there are now experimental reports of an energy gap opening at low temperatures, which has been ascribed to interactions effects [18,19,20,21,22,23,24,25]. Obviously, the possibilities for superconductivity in graphene have also been explored.…”

Evidence for a spin phase transition at charge neutrality in bilayer graphene

“…In particular, a quantum spin Hall analogue has been predicted at ν = 0 in bilayer graphene if the ground state is a spin ferromagnet 8,9 . Previous studies have demonstrated that the bilayer ν = 0 state is an insulator in a perpendicular magnetic field [10][11][12][13][14][15][16] , though the exact nature of this state has not been identified. Here we present measurements of the ν = 0 state in a dual-gated bilayer graphene device in tilted magnetic field.…”

“…The application of an in-plane magnetic field and perpendicular electric field allows us to map out a full phase diagram of the ν = 0 state as a function of experimentally tunable parameters. At large in-plane magnetic field we observe a quantum phase transition to a metallic state with conductance of order 4e 2 /h, consistent with predictions for the ferromagnet.Under a strong perpendicular magnetic field, bilayer graphene (BLG) develops a ν = 0 quantum Hall (QH) state at the charge neutrality point (CNP) which displays anomalous insulating behavior [10][11][12][13][14][15][16] . Transport studies in a dual-gated geometry 12-14 indicate that this gapped state results from an interaction-driven spontaneous symmetry breaking in the valley-spin space 17 .…”

Fine structure of the lowest Landau level in suspended trilayer graphene

“…4(a), the resistance at the CNP decreases as a function of B /k B T , similar to a recent observation in a suspended BLG sample. 33 This decrease suggests that the gap is suppressed by a magnetic field, = 0 − (B). Assuming a simple Zeeman gap, (B) = 2μ B B , leads to a field dependence shown by the solid lines in Fig.…”