Experimental evidence for orbital magnetic moments generated by moiré-scale current loops in twisted bilayer graphene

Abstract

A remarkable property of twisted bilayer graphene (TBG) with small twist angle is the presence of a well-defined and conserved low-energy valley degrees of freedom 1 , which can potentially bring about new types of valley-associated spontaneous-symmetry breaking phases. Electron-electron (e-e) interactions in the TBG near the magic angle ~ 1.1º can lift the valley degeneracy, allowing for the realization of orbital magnetism and topological phases 2-11 . However, direct measurement of the orbital-based magnetism in the TBG is still lacking up to now. Here we report evidence for orbital magnetic moment generated by the moiréscale current loops in a TBG with a twist angle θ ~ 1.68º . The valley degeneracy of the 1.68º TBG is removed by e-e interactions when its low-energy van Hove singularity (VHS) is nearly half filled. A large and linear response of the valley splitting to magnetic fields is observed, attributing to coupling to the large orbital magnetic moment induced by chiral current loops circulating in the moiré pattern.According to our experiment, the orbital magnetic moment is about 10.7 B per moiré supercell. Our result paves the way to explore magnetism that is purely orbital in slightly twisted graphene system.

Recent progresses of quantum confinement in graphene quantum dots

“…This gap is quite larger than the pure Coulomb gap for a system with comparable size [191], which indicates there is a significant spin splitting of triangulene [186]. The tip-assisted method in this work is also proved to be an effective way to manipulate the structure or property of 2D materials, which is widely used in other researches until now [134,[192][193][194].…”

Chirality-Induced Giant Unidirectional Magnetoresistance in Twisted Bilayer Graphene

“… 60 , 61 , 62 It will be intriguing to investigate the UMR effect in the presence of superconductivity for TBG. Furthermore, in experiment magic-angle TBG can exhibit orbital ferromagnetism 6 , 7 , 8 , 14 , 63 , 64 , 65 due to the electron-electron interaction. 30 , 56 , 66 , 67 , 68 , 69 , 70 We point out that the orbital magnetism also leads to UMR where it plays the same role as the magnetic field.…”

Look-alike Landau levels in locally biased twisted bilayer graphene

“…18 Flattening of low energy bands decreases their bandwidths making single particle kinetic energy comparable with electron-electron interactions in TBLG. That gives rise to spectacular correlations effects observed experimentally in recent years such as unconventional superconductivity, 19,20 correlated insulating phases, 21,22 large orbital magnetism 2,23,24 and anomalous Hall ferromagnetism. 25,26 Since TBLG enables engineering single particle properties, what results directly from dependence of Moire energy bands on twist angle, its remarkable features can be fine tuned giving rise to twisttronics.…”

“…Twisted bilayer graphene belong to class of layered van der Waals materials 1 and it is prepared by placing one graphene layer onto another, by means of CVD, pick-up or MBE techniques, [2][3][4][5][6] that the crystallographic axes in both layers differ by small twist angle θ. Honeycomb graphene lattice is composed of two interpenetrating triangle A and B sublattices of carbon atoms and these, due to the twist angle, periodically move closer to and away from their counterparts in second layer leading to formation of Moire lattice. That introduces new length scale L m = a 0 /2/ sin(θ/2) (a 0 = 0.246 nm is graphene lattice constant) defining thus spatial periodicity of interlayer, or more precisely, AA and AB/BA intersublattice couplings.…”