Engineering Proximity Exchange by Twisting: Reversal of Ferromagnetic and Emergence of Antiferromagnetic Dirac Bands in Graphene/Cr$_2$Ge$_2$Te$_6$

Zollner, Klaus; Fabian, Jaroslav

doi:10.48550/arxiv.2108.03984

Cited by 5 publications

(7 citation statements)

References 54 publications

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“…Note that, similar to the TMDCs, CGT also shows a strain-tunable band gap [121][122][123]. Again, the twist angle is crucial for proximity exchange in graphene/CGT heterostructures [40]. In our geometries, the relative twist angle between top (bottom) CGT and the top (bottom) graphene layer is 30 • .…”

Section: A Geometry Setupmentioning

confidence: 72%

“…In Ref. [40], it has been explicitly shown by DFT calculations, that mainly twisting influences proximity exchange, while straining determines the position of the graphene Dirac states within the CGT band gap. This band offset is again tunable by gating, thereby influencing proximity exchange.…”

Section: A Geometry Setupmentioning

confidence: 99%

“…Recently, it has been demonstrated that superconductivity [8][9][10], magnetism [11][12][13][14][15][16][17][18][19][20][21][22][23], and spin-orbit coupling (SOC) [24][25][26][27][28][29][30][31][32][33], can be induced on demand in such weakly glued vdW multilayers. In addition, gating, twisting, stacking, and straining are efficient tunability knobs to tailor these spin interactions [13,28,30,[34][35][36][37][38][39][40][41], while the individual materials also preserve a great degree of autonomy.…”

Section: Introductionmentioning

confidence: 99%

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Proximity spin-orbit and exchange coupling in ABA and ABC trilayer graphene van der Waals heterostructures

Zollner,

Gmitra,

Fabian

2022

Preprint

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We investigate the proximity spin-orbit and exchange couplings in ABA and ABC trilayer graphene encapsulated within monolayers of semiconducting transition-metal dichalcogenides and the ferromagnetic semiconductor Cr2Ge2Te6. Employing first-principles calculations we obtain the electronic structures of the multilayer stacks and extract the relevant proximity-induced orbital and spin interaction parameters by fitting the low-energy bands to model Hamiltonians. We also demonstrate the tunability of the proximity effects by a transverse electric field. Using the model Hamiltonians we also study mixed spin-orbit/exchange coupling encapsulation, which allows to tailor the spin interactions very efficiently by the applied field. We also summarize the spin-orbit physics of bare ABA, ABC, and ABB trilayers, and provide, along with the first-principles results of the electronic band structures, density of states, spin splittings, and electric-field tunabilities of the bands, qualitative understanding of the observed behavior and realistic model parameters as a resource for model simulations of transport and correlation physics in trilayer graphene.

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Section: A Geometry Setupmentioning

confidence: 72%

Section: A Geometry Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Proximity spin-orbit and exchange coupling in ABA and ABC trilayer graphene van der Waals heterostructures

Zollner,

Gmitra,

Fabian

2022

Preprint

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“…Twistronics is now demonstrating its potential for proximity effects. It is revealed that twisting has profound influences on both the magnitude and the type of proximity induced SOC in graphene/TMDC heterostructure [61] as well as proximity exchange coupling in graphene/Cr 2 Ge 2 Te 6 heterostructure and emergence of antiferromagnetic Dirac bands in graphene [62]. Remarkably, wide tunability of the proximity exchange coupling has been reported in TMDC/CrI 3 heterostructures through controlling the interlayer twist between layers and electrostatic gating [63].…”

Section: Introductionmentioning

confidence: 99%

Electrical and thermal transport in a twisted heterostructure of transition metal dichalcogenide and CrI$_3$ connected to a superconductor

Majidi,

Asgari

2022

Preprint

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Wide tunability of the proximity exchange effect between transition metal dichalcogenides (TMDCs) and Chromium trichloride (CrI3) heterostructures provides fascinating opportunity for using TMDCs in two-dimensional magnetoelectrics. In this paper, the effect of the twist angle between the monolayer CrI3 and the TMDC layer as well as the gate electric field on the electrical and thermal transport through a TMDC/CrI3-superconducting TMDC junction are investigated by making use of Dirac-Bogoliubov-de Gennes equation. We show substantial quantities can be controlled by spin-splitting of band structures owing to the spin-orbit interaction, and exchange splitting of the bands originates from the proximity effect. The property of Andreev reflection process strongly depends on the spin-valley polarized states owing to the spin-orbit coupling. Perfect Andreev reflection is possible over a large bias voltage range by using a gate voltage to tune the local Fermi energy and varying the type of charge doping. It is detected that the proposed structure with p-type doping has greater spin-valley polarized Andreev conductance and the high thermal conductance. We further demonstrate that twisting can lead to the suppression or enhancement of the Andreev conductance depending on the chemical potential of the TMDC/CrI3 layer as well as the amplification of the thermal conductance for the chemical potentials less than that of the superconducting region.

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“…The discovery of superconductivity in magic-angle twisted bilayer graphene [40][41][42][43] gave the impetus for twistronics [44][45][46][47], recognizing the twist angle as a critical new control parameter for tailoring electronic properties of van der Waals heterostructures [48][49][50][51][52]. It is then natural to ask how does the twist angle influence proximity SOC in graphene.…”

Section: Introductionmentioning

confidence: 99%

Twist-angle dependent proximity induced spin-orbit coupling in graphene/transition-metal dichalcogenide heterostructures

Naimer,

Zollner,

Gmitra

et al. 2021

Preprint

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We investigate the proximity-induced spin-orbit coupling in heterostructures of twisted graphene and monolayers of transition-metal dichalcogenides (TMDCs) MoS2, WS2, MoSe2, and WSe2 from first principles. We identify strain, which is necessary to define commensurate supercells, as the key factor affecting the band offsets and thus magnitudes of the proximity couplings. We establish that for biaxially strained graphene the band offsets between the Dirac point and conduction (valence) TMDC bands vary linearly with strain, regardless of the twist angle. This relation allows to identify the apparent zero-strain band offsets and find a compensating transverse electric field correcting for the strain. The resulting corrected band structure is then fitted around the Dirac point to an established spin-orbit Hamiltonian. This procedure yields the dominant, valley-Zeeman and Rashba spin-orbit couplings. The magnitudes of these couplings do not vary much with the twist angle, although the valley-Zeeman coupling vanishes for 30°and Mo-based heterostructures exhibit a maximum of the coupling at around 20°. The maximum for W-based stacks is at 0°. The Rashba coupling is in general weaker than the valley-Zeeman coupling, except at angles close to 30°. We also identify the Rashba phase angle which measures the deviation of the in-plane spin texture from tangential, and find that this angle is very sensitive to the applied transverse electric field. We further discuss the reliability of the supercell approach with respect to atomic relaxation (rippling of graphene), relative lateral shifts of the atomic layers, and transverse electric field.

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Engineering Proximity Exchange by Twisting: Reversal of Ferromagnetic and Emergence of Antiferromagnetic Dirac Bands in Graphene/Cr$_2$Ge$_2$Te$_6$

Cited by 5 publications

References 54 publications

Proximity spin-orbit and exchange coupling in ABA and ABC trilayer graphene van der Waals heterostructures

Proximity spin-orbit and exchange coupling in ABA and ABC trilayer graphene van der Waals heterostructures

Electrical and thermal transport in a twisted heterostructure of transition metal dichalcogenide and CrI$_3$ connected to a superconductor

Twist-angle dependent proximity induced spin-orbit coupling in graphene/transition-metal dichalcogenide heterostructures

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