Fractional topological phases and broken time reversal symmetry in strained graphene

Details Fractional topological phases and broken time reversal symmetry in strained graphene Fractional topological phases and broken time reversal symmetry in strained graphene

2011-11-15

arxiv.org/abs/1111.3640v1

Physics

Condensed Matter

Strongly Correlated Electrons

11 pages, 5 figures

Scientific paper

Recently several lattice models with topologically nontrivial flat bands have been shown to host phases such as fractional Chern insulators and fractional topological insulators. Despite wide interest, an experimentally viable system with these exotic topological orders is still lacking. On the other hand a recent experiment has confirmed that strain can be used to control the electronic states of graphene and create flat pseudo-Landau levels in the absence of external magnetic field. These pseudomagnetic fields respect time reversal symmetry and far exceed the strongest magnetic fields available. Here we show that graphene under strain is a natural playground in the search for exotic many-body phases, such as fractional topological insulators and flat band superconductors, in addition to fractional Hall states. At fractional filling, Coulomb interactions stabilize a valley polarized Laughlin liquid that spontaneously breaks time reversal symmetry. On tuning the short ranged interactions, a valley unpolarized fractional phase emerges, which is a time reversal symmetric analog of the Laughlin liquid. Further tuning interactions leads to a spin triplet superconductor. On raising the filling to the neutrality point, we find either a ferromagnet or a valley polarized state, depending on the strength of on-site interactions. The importance of interaction engineering to realize these phases introduces directions for future experimental research to tune interactions in strained graphene as well as in other potential platforms such as patterned electron gases and cold atoms in hexagonal lattices.

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