TY - JOUR

T1 - Quantum spin hall effect in twisted bilayer graphene

AU - Finocchiaro, Francesca

AU - Guinea, F.

AU - San-Jose, P.

PY - 2017/2/1

Y1 - 2017/2/1

N2 - Motivated by a recent experiment (Sanchez-Yamagishi et al 2016 Nat. Nanotechnol.214) reporting evidence of helical spin-polarized edge states in layer-biased twisted bilayer graphene under a magnetic flux, we study the possibility of stabilising a quantum spin Hall (QSH) phase in such a system, without Zeeman or spin-orbit couplings, and with a QSH gap induced instead by electronic interactions. We analyse how magnetic flux, electric field, interlayer rotation angle, and interactions (treated at a mean field level) combine to produce a pseudo-QSH with broken time-reversal symmetry, and spin-polarized helical edge states. The effect is a consequence of a robust interactioninduced ferrimagnetic ordering of the quantum Hall ground state under an interlayer bias, provided the two rotated layers are effectively decoupled at low energies. We discuss in detail the electronic structure and the constraints on system parameters, such as the angle, interactions and magnetic flux, required to reach the pseudo-QSH phase. We find, in particular, that purely local electronic interactions are not sufficient to account for the experimental observations, which demand at least nearest-neighbour interactions to be included.

AB - Motivated by a recent experiment (Sanchez-Yamagishi et al 2016 Nat. Nanotechnol.214) reporting evidence of helical spin-polarized edge states in layer-biased twisted bilayer graphene under a magnetic flux, we study the possibility of stabilising a quantum spin Hall (QSH) phase in such a system, without Zeeman or spin-orbit couplings, and with a QSH gap induced instead by electronic interactions. We analyse how magnetic flux, electric field, interlayer rotation angle, and interactions (treated at a mean field level) combine to produce a pseudo-QSH with broken time-reversal symmetry, and spin-polarized helical edge states. The effect is a consequence of a robust interactioninduced ferrimagnetic ordering of the quantum Hall ground state under an interlayer bias, provided the two rotated layers are effectively decoupled at low energies. We discuss in detail the electronic structure and the constraints on system parameters, such as the angle, interactions and magnetic flux, required to reach the pseudo-QSH phase. We find, in particular, that purely local electronic interactions are not sufficient to account for the experimental observations, which demand at least nearest-neighbour interactions to be included.

KW - Interactions

KW - Landau levels

KW - Majorana modes

KW - Quantum spin Hall

KW - Topology

KW - Twisted bilayer graphene

UR - http://www.scopus.com/inward/record.url?scp=85021669938&partnerID=8YFLogxK

U2 - 10.1088/2053-1583/aa5265

DO - 10.1088/2053-1583/aa5265

M3 - Article

AN - SCOPUS:85021669938

VL - 4

JO - 2 D Materials

JF - 2 D Materials

SN - 2053-1583

IS - 2

M1 - 025027

ER -