Graphene is a good candidate for protective material owing to its extremely high stiffness and high strength-to-weight ratio. However, the impact performance of twisted bilayer graphene is still obscure. Herein we have investigated the ballistic resistance capacity of twisted bilayer graphene compared to that of AA-stacked bilayer graphene using molecular dynamic simulations. The energy propagation processes are identical, while the ballistic resistance capacity of the twisted bilayer graphene is almost two times larger than the AA-bilayer graphene. The enhanced capacity of the twisted bilayer graphene is assumed to be caused by the mismatch between the two sheets of graphene, which results in earlier fracture of the first graphene layer and reduces the possibility of penetration.

Ultrahigh Ballistic Resistance of Twisted Bilayer Graphene

We consider a chiral spin liquid constructed using the parton theory. This state supports non-Abelian anyons and neutral fermions, which share some similarities with the celebrated Moore-Read state. The edge physics of the parton state and the Moore-Read state is very diﬀerent. Based on conformal ﬁeld theory (CFT) analysis, it is proposed that the edge states exhibit an emergent SO(5) symmetry. The counting of edge states in the low-lying SO(5) 1 CFT towers is computed. The chiral spin liquid is generated using tensor network methods, which allows us to conﬁrm the SO(5) 1 counting using entanglement spectrum. An additional feature of multiple branches in the entanglement spectrum is observed and analyzed.

Non-Abelian topological order with SO(5)$_{1}$ chiral edge states

We study the ν = ± 1 / 2 fractional quantum Hall states in graphene observed by Zibrov et al. [Nat. Phys. 14, 930 (2018)]. The parton construction is employed to provide a valley unpolarized trial wave function for these states. The lattice scale valley anisotropic terms in the Hamiltonian soften the repulsion between electrons in different valleys to favor the valley unpolarized state. The validity of our proposal is corroborated by numerical calculations.

Two-component parton fractional quantum Hall state in graphene

Motivated by the experiments on double monolayer graphene that observe a variety of fractional quantum Hall states [Liu et al., Nat. Phys. 15, 893 (2019); Li et al., Nat. Phys. 15, 898 (2019)], we study the special setting in which two monolayers have different areas. It has not been considered before and allows us to construct a class of exotic topological states. The elementary excitations of these states do not carry fractional charges but obey fractional statistics. This is in sharp contrast to all previously studied cases, where the two properties are intimately connected and serve as hallmarks of fractional quantum Hall states. Numerical calculations are performed to demonstrate that some states can be realized with realistic parameters.

https://scipost.org/10.21468/SciPostPhys.13.4.094/pdf

Topological states in double monolayer graphene

At half-filled Landau level, composite fermions with chiral p-wave pairing will form Moore-Read state which hosts charge-e/4 fractional excitation, this excitation support non-Abelian statistics and have potential to enable topological quantum computation. Due to the SU(4) symmetry of electron and electric-field tunability, bilayer graphene become an ideal platform for exploring physics of multi-component quantum Hall state and is candidate for realizing non-Abelian statistics. In this paper, high-quality bilayer graphene/hBN heterostructure is fabricated by using dry-transfer technique, and electric transport measurement is performed to study quantum Hall state behavior in bilayer graphene under electric field and magnetic field。Under strong magnetic field, sequences of incompressible state with quantized Hall conductivity are revealed at -5/2, -1/2, 3/2 filling of Landau level.The feature of even-denominator quantum Hall state manifests more visible then weaker with increasing magnetic field and this correspond to the polarization of Landau level wave function. The experimental results imply the observed even-denominator fractional quantum Hall state belong to the topological phase described by Pfaffian wavefunction.

Wang Zhu

Papers

Even-denominator fractional quantum Hall state in bilayer graphene