Interaction-Driven Spectrum Reconstruction in Bilayer Graphene

Abstract

The nematic phase transition in electronic liquids, driven by Coulomb interactions, represents a new class of strongly correlated electronic ground states. We studied suspended samples of bilayer graphene, annealed so that it achieves very high quasiparticle mobilities (greater than 10(6) square centimers per volt-second). Bilayer graphene is a truly two-dimensional material with complex chiral electronic spectra, and the high quality of our samples allowed us to observe strong spectrum reconstructions and electron topological transitions that can be attributed to a nematic phase transition and a decrease in rotational symmetry. These results are especially surprising because no interaction effects have been observed so far in bilayer graphene in the absence of an applied magnetic field.

Chirald-wave superconductivity in doped graphene

“…Consequently, the semi-metallic dispersion of the honeycomb lattice remains robust for weak interactions and no long-range order occurs even at T = 0. It is currently believed that monolayer pristine graphene is in this parameter regime, as no indications for spontaneous longrange ordering or energy gap opening have so far been found experimentally [63,64,20].…”

“…For example, magnetism has experimentally been reported both in nanographene [58,59,60], and in graphite in the presence of disorder [61] or grain boundaries [62], although pristine graphene has not been found to be either magnetic [63] or gapped [64,20]. Theoretically, on-site Coulomb repulsion exceeding U > 3.9t has been found to give an antiferromagnetic state in undoped graphene in quantum Monte Carlo simulations [15,17].…”

“…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.…”

Transport gap in suspended bilayer graphene at zero magnetic field

“…2,3 Recent advances in obtaining suspended bilayer graphene devices with charge carrier mobility exceeding μ > 10 000 cm 2 V −1 s −1 gave access to the investigation of many-body phenomena in clean bilayer graphene at low charge carrier concentration (n < 10 10 cm −2 ). [4][5][6][7][8][9][10][11] Due to the nonvanishing density of states at the charge neutrality point (CNP), bilayer graphene is predicted to have a variety of ground states triggered by electron-electron interaction. There are two competing theories describing the ground state of BLG: a transition (i) to a gapped layer-polarized state [12][13][14][15][16][17] (excitonic instability) or (ii) to a gapless nematic phase.…”