Untying the insulating and superconducting orders in magic-angle graphene

Stepanov, Petr; Das, Ipsita; Lu, Xiaobo; Fahimniya, Ali; Watanabe, Kenji; Koppens, Frank H. L.; Lischner, Johannes; Levitov, Leonid; Efetov, Dmitri K.

doi:10.1038/s41586-020-2459-6

Cited by 489 publications

(388 citation statements)

References 35 publications

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“…However, in doing so, addressing the role of electronic interaction has been a major challenge for theorists and experimentalists alike. Attempts to control the insulating or superconducting states by controlling interaction [8][9][10], or otherwise [9,[11][12][13][14][15][16][17][18][19], have led to a surprisingly large number of dissimilar phase diagrams of TBG. In fact, even the number of insulating regions and that of the superconducting domes in these samples (under almost equivalent external circumstances) has been widely different.…”

Section: Introductionmentioning

confidence: 99%

Transport across twist angle domains in moiré graphene

Padhi

Tiwari

Neupert

et al. 2020

Phys. Rev. Research

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Many experiments in twisted bilayer graphene (TBG) differ from each other in terms of the details of their phase diagrams. Few controllable aspects aside, this discrepancy is largely believed to arise from the presence of a varying degree of twist angle inhomogeneity across different samples. Real-space maps indeed reveal TBG devices splitting into several large domains of different twist angles. Motivated by these observations, we study the quantum mechanical tunneling across a domain wall (DW) that separates two such regions. We show that the tunneling of the moiré particles can be understood by the formation of an effective step potential at the DW. The height of this step potential is simply a measure of the difference in twist angles. These computations lead us to identify the global transport signatures for detecting and quantifying the local twist angle variations. In particular, using Landauer-Büttiker formalism, we compute single-channel conductance (dI/dV) and Fano factor for shot noise (ratio of noise power and mean current). A reduction in the low-energy conductance and a zero-bias sub-meV gap in the conductance are observed which scale with the twist angle difference. One of the key findings of our work is that transport in presence of twist angle inhomogeneity is "noisy," though sub-Poissonian. In particular, the differential Fano factor peaks near the van Hove energies corresponding to the domains in the sample. The location and the strength of the peak are simply a measure of the degree of twist angle inhomogeneity.

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Section: Introductionmentioning

confidence: 99%

Transport across twist angle domains in moiré graphene

Padhi

Tiwari

Neupert

et al. 2020

Phys. Rev. Research

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“…Both states have been previously observed only for angles within ±0.1°from the magic-angle value and occur in adjacent or overlapping electron density ranges; nevertheless, it is still unclear how the two states are related. Beyond the twist angle and strain, the dependence of the TBG phase diagram on the alignment 4,6 and thickness of insulating hexagonal boron nitride (hBN) 7,8 used to encapsulate the graphene sheets indicates the importance of the microscopic dielectric environment. Here we show that adding an insulating tungsten-diselenide (WSe 2 ) monolayer between hBN and TBG stabilizes superconductivity at twist angles much smaller than the established magic-angle value.…”

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confidence: 99%

“…However, in such devices the band structure of the flat bands is strongly altered 6 , and superconductivity-typically observed when hBN and TBG are misaligned-is absent. Recent work using a very thin hBN layer separating a back gate from TBG additionally suggests that electrostatic screening plays a prominent role in the appearance of insulating and superconducting states 7 . These experiments exemplify the effects of hBN layers on the phase diagram in hBN-TBG-hBN structures and highlight the importance of understanding how microscopic details of the dielectric environment alter the properties of correlated phases.…”

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confidence: 99%

Superconductivity in metallic twisted bilayer graphene stabilized by WSe2

Arora

Polski

Zhang

et al. 2020

Nature

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“…Nevertheless, magic angle flat bands in tBLG are topologically nontrivial [57][58][59][60] , interpreted in terms of the pseudo magnetic fields generated by the moiré potential 60 . Quantum anomalous Hall effect was observed in magic angle tBLG on hexagonal Boron Nitride (hBN) substrate [61][62][63] . The Hall effect in tBLG, however, is present only at the magic angle and cannot be tuned through the twist angle.…”

Section: Discussionmentioning

confidence: 99%

Magnon magic angles and tunable Hall conductivity in 2D twisted ferromagnetic bilayers

Ghader

2020

Sci Rep

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Twistronics is currently one of the most active research fields in condensed matter physics, following the discovery of correlated insulating and superconducting phases in twisted bilayer graphene (tBLG). Here, we present a magnonic analogue of tBLG. We study magnons in twisted ferromagnetic bilayers (tFBL) with collinear magnetic order, including exchange and weak Dzyaloshinskii-Moriya interactions (DMI). For negligible DMI, tFBL presents discrete magnon magic angles and flat moiré minibands analogous to tBLG. The DMI, however, changes the picture and renders the system much more exotic. The DMI in tFBL induces a rich topological magnon band structure for any twist angle. The twist angle turns to a control knob for the magnon valley Hall and Nernst conductivities. Gapped flat bands appear in a continuum of magic angles in tFBL with DMI. In the lower limit of the continuum, the band structure reconstructs to form several topological flat bands. The luxury of twist-angle control over band gaps, topological properties, number of flat bands, and valley Hall and Nernst conductivities renders tFBL a novel device from fundamental and applied perspectives.

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Untying the insulating and superconducting orders in magic-angle graphene

Cited by 489 publications

References 35 publications

Transport across twist angle domains in moiré graphene

Transport across twist angle domains in moiré graphene

Superconductivity in metallic twisted bilayer graphene stabilized by WSe2

Magnon magic angles and tunable Hall conductivity in 2D twisted ferromagnetic bilayers

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