Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle

Codecido, Emilio; Wang, Qiyue; Koester, Ryan; Che, Shi; Tian, Haidong; Lv, Rui; Tran, Son; Watanabe, Kenji; Taniguchi, Takashi; Zhang, Fan; Bockrath, Marc; Lau, Chun Ning

doi:10.1126/sciadv.aaw9770

Cited by 201 publications

(151 citation statements)

References 51 publications

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“…Spurred by the discovery of a plethora of insulating and superconducting states in twisted bilayer graphene (TBG) [1,2], a growing stream of experimental evidence points to the generic emergence of correlated electronic behavior in various moiré heterostructures [3][4][5][6][7][8][9][10][11][12]. The basic mechanism that gives rise to strongly-enhanced correlation effects in these materials is the formation of long-wavelength moiré patterns with (almost) flat lowenergy bands whose narrow bandwidth becomes comparable to the otherwise negligible energy scale of the electronic interactions [13][14][15].…”

mentioning

confidence: 99%

Emergence and stability of spin-valley entangled quantum liquids in moiré heterostructures

Kiese

Buessen

Hickey

et al. 2020

Phys. Rev. Research

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Twisting moiré heterostructures to the flatband regime allows for the formation of strongly correlated quantum states, since the dramatic reduction of the bandwidth can cause the residual electronic interactions to set the principal energy scale. An effective description for such correlated moiré heterostructures, derived in the strong-coupling limit at integer filling, generically leads to spin-valley Heisenberg models. Here we explore the emergence and stability of spin liquid behavior in an SU(2) spin ⊗ SU(2) valley Heisenberg model upon inclusion of Hund's-induced and longer-ranged exchange couplings, employing a pseudofermion functional renormalization group approach. We consider two lattice geometries, triangular and honeycomb (relevant to different moiré heterostructures), and find, for both cases, an extended parameter regime surrounding the SU(4) symmetric point where no long-range order occurs, indicating a stable realm of quantum spin liquid behavior. For large Hund's coupling, we identify the adjacent magnetic orders, with both antiferromagnetic and ferromagnetic ground states emerging in the separate spin and valley degrees of freedom. For both lattice geometries the inclusion of longer-ranged exchange couplings is found to have both stabilizing and destabilizing effects on the spin liquid regime depending on the sign of the additional couplings.

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confidence: 99%

Emergence and stability of spin-valley entangled quantum liquids in moiré heterostructures

Kiese

Buessen

Hickey

et al. 2020

Phys. Rev. Research

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“…where 0 is the intrinsic diffusivity of copper, E is the activation energy of copper, T is the growth temperature in Kelvin, is the Boltzmann constant. From literature, 0 = 5.6 × 10 −7 2 / and = 0.92 5,6. Hence, the diffusion coefficient of carbon into copper at our growth temperature (1050 ℃) is 175 nm2/s.…”

Section: Supplementary Textmentioning

confidence: 79%

Frank-van der Merwe Growth in Bilayer Graphene

Wang¹,

Yao²,

Leong³

et al. 2020

Preprint

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<p>Bilayer graphene has attracted interest for its unique properties, including interesting electrical behavior when one layer is slightly rotated relative to the other. However, the quality of large-area bilayer graphene is often limited by the layer-plus-island growth mode in which islands of thicker graphene present as unavoidable impurities. Here, we report the observation of the layer-by-layer, Frank-van der Merwe (FM) growth mode in bilayer graphene where multilayer impurities are suppressed. Instead of the conventional surface adhesive energy, it is found that interface adhesive energy is possible to be tuned with an oxidative pretreatment. The FM-grown bilayer graphene is of AB-stacking or with small-twisting-angle (θ = 0-5°), which is more mechanically robust compared to monolayer graphene, facilitating a free-standing wet transfer technology.</p>

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“…by rotation of 2 stacked SLG sheets to form a Moiré superlattice. For instance, Cao et al [7] showed that MATBG with  = 1.16° exhibits zero resistance at Tc = 0.14 K, whereas an angle  = 1.05° has zero resistance at Tc ~ 1.2 K. More recently, several research groups have discovered a superconducting state in MATBG [8][9][10][11], including studies of MATBG at high-pressures (up to P = 4 GPa), as well as in trilayer graphene/boron nitride Moiré superlattices [12].…”

Section: Introductionmentioning

confidence: 99%

Classifying superconductivity in Moiré graphene superlattices

Talantsev

Mataira

Crump

2020

Sci Rep

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Several research groups have reported on the observation of superconductivity in bilayer graphene structures where single atomic layers of graphene are stacked and then twisted at angles forming Moiré superlattices. The characterization of the superconducting state in these 2D materials is an ongoing task. Here we investigate the pairing symmetry of bilayer graphene Moiré superlattices twisted at  = 1.05°, 1.10° and 1.16° for carrier doping states varied in the range of = 0.5 − 1.5 • 10 12 −2 (where superconductivity can be realized) by analyzing the temperature dependence of the upper critical field Bc2(T) and the self-field critical current Jc(sf,T) within currently available models for single-and two-band s-, d-, pand d+id-wave gap symmetries. Extracted superconducting parameters show that only s-wave and a specific kind of p-wave symmetries are likely to be dominant in bilayer graphene Moiré superlattices. More experimental data is required to distinguish between the s-and remaining p-wave symmetries as well as the suspected two-band superconductivity in these 2D superlattices.

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Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle

Cited by 201 publications

References 51 publications

Emergence and stability of spin-valley entangled quantum liquids in moiré heterostructures

Emergence and stability of spin-valley entangled quantum liquids in moiré heterostructures

Frank-van der Merwe Growth in Bilayer Graphene

Classifying superconductivity in Moiré graphene superlattices

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