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## Creator

Yating Sha, Jian Zheng, Kai Liu, Hong Du, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Jinfeng Jia, Zhiwen Shi, Ruidan Zhong, Guorui Chen

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This is the author’s version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science on Vol 384, 25 Apr 2024, DOI: 10.1126/science.adj8272.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Observation of a Chern insulator in crystalline ABCA-tetralayer graphene with spin-orbit coupling](https://mdr.nims.go.jp/datasets/0d671714-7530-477a-8e82-52732e6c2e31)

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Observation of a Chern insulator in crystalline ABCA-tetralayer graphene with spin-orbit couplingObservation of a Chern insulator in crystallineABCA-tetralayer graphene with spin-orbit couplingYating Sha1†, Jian Zheng1†, Kai Liu1†, Hong Du2, Kenji Watanabe3, Takashi Taniguchi4, Jinfeng Jia1,2,Zhiwen Shi1, Ruidan Zhong2, Guorui Chen1*Degeneracies in multilayer graphene, including spin, valley, and layer degrees of freedom, can belifted by Coulomb interactions, resulting in rich broken-symmetry states. Here, we report aferromagnetic state in charge-neutral ABCA-tetralayer graphene driven by proximity-induced spin-orbit coupling from adjacent tungsten diselenide. The ferromagnetic state is identified as a Cherninsulator with a Chern number of 4; its maximum Hall resistance reaches 78% quantization at zeromagnetic field and is fully quantized at either 0.4 or –1.5 tesla. Three distinct broken-symmetryinsulating states, layer-antiferromagnet, Chern insulator, and layer-polarized insulator, along withtheir transitions, can be continuously tuned by the vertical displacement field. In this system, themagnetic order of the Chern insulator can be switched by three knobs, including magnetic field,electrical doping, and vertical displacement field.Rhombohedral-stackedmultilayergrapheneexhibits highly flat conduction and va-lence bands in the vicinity of the charge-neutral point (CNP), where low-energybands can be approximately described bya two-band model with an energy-momentumdispersion relation of E ~ kN (where E repre-sents energy, k represents momentum, andN is the number of layers) (1–5). As a result,graphene multilayers are anticipated to havestrong Coulomb interactions (6–9). Addition-ally, the low-energy bands in graphene arelargely associatedwithmomentum-space Berrycurvatures (10) and exhibit multiple degener-acies, including spin, valley, and layer degreesof freedom. These degeneracies are believedto be susceptible to symmetry-breaking effectsinduced by interactions (11–15). Therefore, itis predicted that rhombohedral-stackedmulti-layer graphene can host a diverse range ofinteraction-driven broken-symmetry states,including the anticipated Chern insulator phasewhen the top and bottom layers have op-posite valley flavors (12–15). Recent success infabricating high-quality rhombohedral-stackedmultilayer graphene on hexagonal boron ni-tride (hBN) devices provides promising oppor-tunities to investigate the broken-symmetrystates (16–20).When the layer number of graphene increasesto four, the Coulomb interactions become suf-ficiently strong to spontaneously break sym-metries, leading to layer-resolved chargedistribution (layer pseudospin polarization)associated with four spin-valley flavors, incharge-neutral ABCA-tetralayer graphene (ABCA-4LG) on hBN. Recent experiments reporteda layer-antiferromagnetic (LAF) insulator, inwhich the flavors (K↑) and (K′↑) are polarizedin the top layer, with (K↓) and (K′↓) in thebottom layer (where K and K′ correspond totwo valleys, ↑ and ↓ correspond to two spins),in crystalline ABCA-4LG and ABCAB-pentalayergraphene (19–21). Such an LAF insulating stateis absent in the ABC-trilayer on hBN (18, 22). Byapplying a large vertical displacement fieldD, one canmanipulate the charge distributionof the flavors. Thus, one expects the emer-gence of partial and full layer-charge polar-izations, which are associated with quantumanomalous Hall (QAH) and quantum valleyHall (QVH), respectively. Indeed, a continuousphase transition from LAF under balancedlayer-charge polarization to layer polarized in-sulator [LPI, also referred as QVH accordingto certain theory and experimental results(11–13)] under full layer-charge polarizationwas observed when increasing the displace-ment field (19). However, QAH, namely a Cherninsulator, under partial layer-charge polariza-tion, was absent in this experiment.Here, we report ferromagnetism in charge-neutral ABCA-4LG by introducing spin-orbitcoupling (SOC) from an adjacent layer of WSe2.Upon tuning D to the intermediate regionbetween the LAF and LPI states, we observedan anomalous Hall hysteretic loop, exhibitinga large Hall resistance Rxy = 5 kW at zero mag-netic field B. The Rxy value rapidly quantizesto h/4e2 ~ 6.4 kW (where h is Planck’s con-stant and e is the electron’s charge) at a verylowmagnetic field of 0.4 T for positivemagneticfield (and –1.5 T for the negative side), fol-lowing the Streda formulawith aChernnumberC = 4, providing evidence that the ferromag-netic state is a high-order Chern insulator (23).Ferromagnetism in ABCA-tetralayer graphenewith WSe2The presence of ABCA-4LG domains in exfo-liated tetralayer graphene flakes was confirmedusing scanning near-field infrared microscopy(fig. S1). To stabilize its stacking during sub-sequent fabrication processes, the ABCA-4LGdomain was isolated from adjacent ABAB do-mains by cutting using an atomic force mi-croscope. Subsequently, the ABCA-4LG domainwas encapsulated between exfoliated hBN thinfilms, with a monolayer of WSe2 added be-tween ABCA-4LG and the top hBN layer. Theresulting heterostructure was fabricated into aHall bar geometry, featuring one-dimensional(1D) edge contacts, a metal top gate, and adoped silicon bottom gate. Throughout thefabrication procedures, the stacking order ofABCA-4LG under hBN coverage was moni-tored using the phonon-polariton assisted near-field optical imaging technique (fig. S2D) (19).Figure 1A shows an optical image of the de-vice, and Fig. 1B provides a schematic repre-sentation [see sections S1 and S2 of (24) forfurther details on WSe2 crystal growth anddevice fabrication]. The top and bottom gatesenable individual tuning of the doping n andthe vertical displacement fieldD applied to theABCA-4LG [see section S3 of (24)].Transport measurements were conductedon ABCA-4LG both with and without WSe2.In the case of ABCA-4LG without WSe2, asshown in fig. S3A, twopeaks in the longitudinalresistance Rxx are observed at CNP for D = 0and large |D|. These peaks correspond to theinteraction-driven LAF insulator and LPI states,respectively (18, 21). A low-resistance regionnear |D| ~ 0.1 V/nm connects these two in-sulators, indicating a gap closure during thecontinuous phase transition from LAF to LPI.The Hall resistance Rxy at a magnetic field |B| =0.5 T in fig. S3B exhibits the expected signchange across the CNP for the entire range ofD. In ABCA-4LG with WSe2 (Fig. 1C), Rxx dis-plays similar features of LAF and LPI at theCNP for both zero and large |D|. However, inthe Rxy measurement shown in Fig. 1D, at in-termediate values of D near ±0.1 V/nm, thesign change of Rxy shifts toward the positive nside, resulting in a prominent Rxy at the CNP.Considering that the only difference betweenthese two devices is the presence of WSe2, thedistinct nonzero Rxy at the CNP can be attrib-uted to WSe2.To investigate the large Rxy at CNP for in-termediate D in ABCA-4LG with WSe2, wemeasured its magnetic field dependence. Fig-ure 1E clearly shows the hysteretic anomalousHall effect, providing clear evidence for the fer-romagnetism in ABCA-4LG with WSe2. As acomparison, when we performed the same1Key Laboratory of Artificial Structures and Quantum Control(Ministry of Education), Shenyang National Laboratory forMaterials Science, School of Physics and Astronomy,Shanghai Jiao Tong University, Shanghai 200240, China.2Tsung-Dao Lee Institute, Shanghai Jiao Tong University,Shanghai, 201210, China. 3Research Center for Electronicand Optical Materials, National Institute for MaterialsScience, Tsukuba 305-0044, Japan. 4Research Center forMaterials Nanoarchitectonics, National Institute for MaterialsScience, Tsukuba 305-0044, Japan.*Corresponding author. Email: chenguorui@sjtu.edu.cn†These authors contributed equally to this work.1 of 6mailto:chenguorui@sjtu.edu.cnhttp://crossmark.crossref.org/dialog/?doi=10.1126%2Fscience.adj8272&domain=pdf&date_stamp=2024-04-25measurements on ABCA-4LG without WSe2,no ferromagnetic behavior was observed un-der the same conditions (fig. S3D). It is believedthat SOC on the order of milli–electron voltscan be introduced into graphene through prox-imity with WSe2 because of the hybridizationbetween electron wave functions of the twocrystals (25, 26). The hysteresis of Rxy disap-pears as the temperature increases to 11 K(Fig. 1E), which is consistent with the calculatedand experimental estimates of the proximity-induced SOC strength of ~1 meV in twisted orBernal bilayer graphene with WSe2 (27–30).Although the intrinsic SOC in graphene wastheoretically predicted to stabilize a 2D quan-tum spin Hall topological insulator (31), inpractice, the intrinsic SOC is negligible (onthe order of micro–electron volts) (32–34).However, the proximity-induced SOC in graph-ene is significant and has been predicted togive rise to topological phases in multilayergraphene (26, 35).Topological phasesTo explore the topological phase in ABCA-4LGwith SOC, we further cooled down the sampleto T = 0.1 K and performed measurements ofRxy and Rxx as a function of n and B at D =–0.1 V/nm. The anomalous Hall signal at D =+0.1 V/nm was less pronounced (fig. S8); adiscussion of this D↔ −D asymmetry can befound in section S5 of (24). The inset of Fig. 2Cdisplays the hysteresis of Rxy, highlightingthat the Rxy value increases to a maximum of5 kW at zeromagnetic field and T= 0.1 K. Figure2B shows that the largeRxy signal persists overa range of ~–0.1 to 0.4 × 1012 cm−2 and exhibitsa sharp sign reversal near zero magnetic fielddue to the anomalous Hall effect. At a very lowfield of +0.4 T, the Rxy is rapidly quantized at6.4 kW, corresponding to a quantum Hall re-sistance of h/4e2, following the Streda formulan = neB/h for n = 4, where n is the filling factorof Landau levels. The presence of the n = 4quantum Hall state is further evidenced bythe corresponding Rxx fan diagram shown inFig. 2A, where a minimum in Rxx starts todevelop along the slope of the n = 4 quantumHall states, represented by the dashed lines.The observed quantumHall state in the pres-ence of a magnetic field is, in fact, a manifes-tation of the QAH effect in a Chern insulatorwith a Chern number C = 4. First, when sweep-ing the magnetic field back and forth within asmall range of ±0.2 T at CNPandD= –0.1 V/nm,we clearly observed an anomalous Hall sig-nal exhibiting a ferromagnetic hysteresis loop.Themeasured anomalous Hall signals ofRxy =5.0 kW and 3.5 kW for up and down sweeps ofthe magnetic field, respectively, correspondto 78% and 55% of the quantized Rxy value ofh/4e2. We emphasize that the data presentedin themain text are displayed in their raw form,and have not undergone any processing suchas symmetrization or antisymmetrization. Theemergence of the anomalous Hall signal sig-nifies the breaking of time-reversal symmetryand the presence of ferromagnetism, both ofwhich are hallmarks of the Chern insulator(36–41). Second, both the resistance Rxx andthe conductivity sxx at zero magnetic fielddecreasewith decreasing temperature (fig. S7),suggesting the quantum Hall type insulatingbehavior at zero magnetic field. This is indica-tive of the presence of an exchange gap, whichis also consistent with a Chern insulator. Atthe same time, the temperature dependence ofRxy suggests that the incomplete quantizationA B EDCFig. 1. Schematic and transport of ABCA-4LG with WSe2. (A) Optical imageof the hBN/WSe2/ABCA-4LG/hBN device, including a schematic of the transportmeasurement configuration. The Hall bar–shaped graphene is highlighted byred dashed line. Scale bar, 1 mm. (B) Schematic side view of a dual-gate WSe2/ABCA-4LG device. The crystal structures of ABCA-4LG and WSe2 monolayerare shaded by light purple and light orange, respectively. A unit cell of ABCA-4LGis labeled in red. (C and D) Color plot of longitudinal Rxx (C) and Hall Rxy(D) resistance at T = 1.5 K as a function of carrier density n and displacementfield D. Rxx is measured under zero magnetic field, showing insulatingstates at D = 0 V/nm and large |D|. Rxy is measured at a low magnetic field,B = –0.5 T. The dashed rectangles near D = ±0.1 V/nm in (D) outline theregions of Chern insulator, where the sign change of Rxy shifts towardthe positive n side, resulting in a large Rxy at the CNP. The gray and blackregions represent larger and smaller values than the color scales,respectively. (E) Hysteresis loops of anomalous Hall signals at CNP andD = –0.1 V/nm at various temperatures above T = 1.5 K.2 of 6of Hall resistance at zero magnetic field maybe attributed to sample quality issues, for ex-ample, nonuniform proximity-induced SOC(caused by inhomogeneous interface) or de-fects in the WSe2 crystal. Third, only n = 4quantum Hall state emerges within the rangeof ±2 T, which is a characteristic feature of aquantized anomalous Hall state. Otherwise,additional quantum Hall states would be ex-pected to develop (8, 19, 20). Indeed, whentuning D outside the range of the anomalousHall region, a series of quantum Hall statesemerge, as shown in fig. S9. Finally, the Hallangle at zero magnetic field, defined as rxy/rxx, exhibits a large value of 3.6 [which is atleast two orders of magnitude larger than theexpected values for extrinsic mechanisms inmost ferromagnetic materials (42)], indicat-ing an intrinsic mechanism for the anoma-lous Hall and, consequently, the nontrivialband topology.Following upon the discussions on the Cherninsulator, we present the magnetic field-stabilized QAH effect in Fig. 2, C and D. Thelongitudinal and Hall resistances are plottedas a function of the magnetic field along thedashed lines in Fig. 2, A and B, respectively, inaccordance with the Streda formula for aChern number C = ±4. The sign of the Chernnumber is reflected in the sign of Rxy and canbe switched by controlling the magnetic field.The ferromagnetic hysteretic behavior for othervalues of n and D are shown in fig. S10.Breaking symmetryNext, by examining the broken-symmetry statesand their transitions along tuning the displace-ment field for charge-neutral ABCA-4LG withand without WSe2, we were able to gain val-uable insights into the emergence of the Cherninsulator. In the case of ABCA-4LG withoutWSe2, as shown in Fig. 3A and fig. S3, twobroken-symmetry correlated insulating states,LAF and LPI, are observed at CNP. LAF em-erges at D = 0, where two spin-valley flavors,(K↑) and (K ′↑), are polarized in the top layer,whereas the other two flavors, (K↓) and (K ′↓),are polarized in the bottom layer. At largevalues of D, all four spin-valley flavors becomepolarized in the same layer, resulting in theLPI state. Each spin-valley flavor pair corre-sponds to a bandwith a Chern number of ±N/2,where N (=4 for the tetralayer) represents thenumber of graphene layers (13). The sign ofthe Chern number depends on both the valleylabel and the mass term (the sense of layerpolarization) in the two-band model of ABCA-4LG (10, 13). For simplicity, the sign can beconveniently represented by the valley-layerlocking: a positive sign when K(K ′) is polarizedin the top (bottom) layer and a negative signwhen K(K ′) is polarized in the bottom (top)layer. Following this criterion, for LAF, depictedas the gray diagram in Fig. 3C, the Chern num-ber of (K↑), (K ′↑), (K↓), and (K ′↓) are 2, –2, –2,and 2, respectively, resulting in a zero totalChern number and indicating a topologicaltrivial state. Similarly, for LPI, illustrated asthe blue diagram in Fig. 3C, (K↓) and (K′↓)are transferred from the bottom layer to thetop layer, with the signs of their Chern num-bers reversing and becoming 2 and –2, respec-tively. As a result, the total Chern numberremains zero for LPI (fig. S6). In the interme-diate region between LAF and LPI, Rxx con-tinuously decreases to as low as ~2 kW andexhibits metallic temperature dependence atlow temperatures (fig. S3C). Additionally, noanomalous Hall effect is observed (fig. S3, BandD), indicating a gap closure at D~0.1V/nm.These broken-symmetry insulating states inABCA-4LG without WSe2 are driven by strongCoulomb interactions in the intrinsic flat bandsof ABCA-4LG, which allows the breaking ofABC DFig. 2. Chern insulator and magnetic field–stabilized QAH effect atD = –0.1 V/nm. (A and B) Color plot of Rxx (A) and Rxy (B) as a function ofcarrier density n and magnetic field B at D = −0.1 V/nm and T = 0.1 K. Then = 4 quantum Hall state can be identified following the Streda formula (denotedby the red dashed lines). Near zero magnetic field, Rxy exhibits a sharp signreversal, indicating the presence of the anomalous Hall effect. Field is sweptfrom positive to negative (namely sweeping down) in both plots. (C andD) Magnetic field–dependent Rxx and Rxy at D = −0.1 V/nm. Data within asmall range of B = ±0.2 T are collected from continuous B sweeping up anddown [see inset of (C) for magnification]. At higher B fields, data points (emptycircles) of Rxx and Rxy are acquired along the dashed lines in (A) and (B) followingthe Streda formula.3 of 6ABCFig. 3. Broken-symmetry states at CNP in ABCA-4LG with and withoutSOC. (A) Rxx as a function of D at B = 0 T in ABCA-4LG without SOC (WSe2).Gray and blue shaded regions correspond to the interaction-driven LAF andLPI states, respectively. (B) Rxy as a function of D at B = 0 T in ABCA-4LGwith SOC (WSe2). In addition to LAF and LPI states, the CI states are observedwith hysteresis loops at D = ±0.1 V/nm (orange shaded regions in the toppanel). The bottom panel shows a magnified plot of Rxy in linear scale. Insetschematics in (A) and (B) indicate the layer polarization of spin-valley flavors fordifferent broken-symmetry states (for the CI state, only one representativepolarization phase is presented; the complete phase diagram is shown in fig.S13). The black and gray lines in the inset represent four graphene layers. Valleysand spins are represented by K, K′, and ↓, ↑. (C) Schematics of the Chernnumbers and Hall conductivity contributions of four spin-valley flavor pairs fordifferent broken-symmetry states. Each spin-valley flavor pair corresponds toa band with a Chern number of ±2, denoted by solid (+2) or dashed (–2) bandsin the bottom panels, respectively. The directions (left and right) of the arrowsin the top panels represent the corresponding Hall conductivity contributions(+2e2/h and –2e2/h). Only holes in the occupied valence band are consideredhere. A more comprehensive diagram is shown in figs. S5 and S6 for ABCA-4LGwith and without WSe2, respectively.4 of 6time-reversal symmetry (T ) and inversion sym-metry (I) while preserving the valley-Ising sym-metry (Z2) (13, 43), leading to the absence ofChern insulator.By comparison, Fig. 3B shows Rxy as a func-tion of D at CNP for ABCA-4LG with WSe2(fig. S4 shows a direct comparison of Rxy-Ddata in ABCA-4LG with and without WSe2).As D is swept, the LAF and LPI states are notevidently affected by SOC because of theirlarge energy gaps (19, 21). However, SOC playsa crucial role in the intermediate state be-tween LAF and LPI, leading to the emergenceof a Chern insulator state. The Chern insulatorcan be attributed to a band inversion of oneflavor pair, driven by the proximity-inducedSOC. At intermediate D = 0.1 V/nm, shown asthe orange diagram in Fig. 3C, (K↓) is trans-ferred from the bottom layer to the top layer,resulting in a sign change of its Chern numberfrom –2 to 2. This sign change leads to a totalChern number of 4 (= 2 + 2 + 2 – 2) whenadding up the Chern numbers of all four flavorpairs. In addition to breaking the time-reversalsymmetry and inversion symmetry, the inter-play of SOC and strong Coulomb interactionscan further break the Z2 symmetry, drivingthe formation of the Chern insulator state. Weprovide a diagram for the detailedmechanismby which SOC stabilizes the Chern insulatorstate in fig. S5.Controlling the magnetic orderThe observed Chern number C = ±4 in ABCA-4LG with WSe2 is compatible with the pre-dicted flavor ferrimagnetic (Fi) state for partiallayer-chargepolarization in rhombohedralmulti-layer graphene. Such states have associated“ALL” quantum Hall phases, including quan-tum anomalous charge, spin, valley, and spin-valley Hall state (hence the name) (fig. S13)(13, 44). Our transport measurements primar-ily detected the quantum anomalous chargeHall effect in ABCA-4LG with SOC, indicating apromising systemfor further explorationofquan-tum anomalous spin, valley, and spin-valleyHall effects using spin- and valley-sensitiveprobes. There are four possible layer-flavorpolarization configurations for the “ALL” stateat a given D (as shown in fig. S13), which cor-respond to different magnetic states, or name-ly the Chern numbers. Therefore, one canexpect to manipulate the magnetic order inthis 3D parameter space (B, n, D).Themagnetic order, represented by the signof the anomalous Hall resistance (DRBxy ¼RB↑xy � RB↓xy), exhibits dependence on n. In Fig.4A, a sign reversal of DRBxy is observed whenn slightly crosses CNP at ~0.28 × 1012 cm−2,indicating a switching of the magnetic orderas the Fermi level crosses the band gap. Figure4B presents representative line cuts from Fig.4A at different n values. The magnetic ordercan be directly switched by tuning n at fixedB. At fixedmagnetic fields ranging from0.28 Tto –0.26 T, hysteresis loops of Rxy in the n-axisare observed, indicating the switching of themagnetic order as n is swept back and forth(Fig. 4D). The sign reversal of DRnxy ¼ Rn↑xy�Rn↓xy occurs when the magnetic field crosseszero (Fig. 4C). This demonstrates that the mag-netic order of the Chern insulator at CNP canbe individually controlled by B and n, as shownin Fig. 4E. Similar electrically tunable magnet-ism in Chern insulators has been reported intwisted graphene systems (45–47), where thenet magnetization has two contributions, onefrom the bulk stemming from a certain valleypolarization and the other from the edge state,which can reverse sign when tuning the dop-ing inside the topological gap (48). However,A B CD EFig. 4. Electrical switching of the magnetic order. (A) Anomalous Hall resistancewhen sweeping B, defined by DRBxy ¼ RB↑xy � RB↓xy and represented by colors,at different dopings near CNP at D = –0.1 V/nm and T = 0.1 K. An abrupt signchange of DRBxy occurs at ~n = 0.28 × 1012 cm−2. (B) Magnetic hysteresis loops ofRxy at n = 0.4 × 1012, 0.32 × 1012, 0.2 × 1012, 0, and –0.08 × 1012 cm−2, with colorscorresponding to the doping positions labeled in (A). Data are vertically offset forclarity. Solid lines on the y axis mark the positions of zero Rxy for each curve. (C) Theanomalous Hall resistance when sweeping n, defined by DRnxy ¼ Rn↑xy � Rn↓xy , atfixed B ranging from –0.26 T to 0.28 T. Temperature and D are the same as in(A). (D) Electrical hysteresis loops of Rxy at B = ±50 mT, with colors correspondingto the magnetic fields labeled in (C). (E) Schematic of two individual knobs, B andn, of tuning the magnetic order of the Chern insulator at CNP in ABCA-4LG.5 of 6in charge-neutral ABCA-4LG with WSe2, themagnetic order originates from both K andK′ valleys, which distinguishes it from themag-netism reported inMoiré systems (fig. S12). Thedetailed mechanism of the electrically tunablemagnetism in such crystalline graphene re-quires further theoretical investigation.The magnetic order also exhibits an inter-esting dependence on the displacement field.Figure 3B (bottom panel) shows hysteresisloops of Rxy in D at the Chern insulator statesfor D = ±0.1 V/nm. When sweeping D fromnegative to positive, Rxy is negative near D =–0.1 V/nm and positive near D = 0.1 V/nm.Conversely, when sweeping D from positiveto negative, Rxy becomes negative near D =0.1 V/nm and positive near D = –0.1 V/nm.However, at a magnetic field of B = 10 mT(-10 mT), unlike the sign reversal observedduring doping switching, Rxy remains posi-tive (negative) for both sweeping directionson both sides of D (fig. S11). The ferromag-netism, and therefore the Chern number inABCA-4LG/WSe2, can be switched by threeknobs, B, n, and D, represented by a 3D pa-rameter space shown in fig. S13.Discussion and outlookWe now discuss the specific properties of theChern insulator state observed in ABCA-4LGwith WSe2. First, its mechanism markedly dif-fers from the Chern insulator states found indoped and/or intrinsic magnetic topologicalinsulators and 2D Moiré superlattices. Thetime-reversal symmetry breaking emerges fromthe strong Coulomb interactions within theintrinsic flat band of crystalline graphene, andthe nontrivial topology arises from the proximity-induced SOC from WSe2. Second, the magne-tism (and the Chern number) in our systemoriginates from both K and K′ valleys in dif-ferent layers rather than from a single valleyas in the Moiré system (fig. S12). Two oppo-site valleys in different layers contribute tothe total Chern number, which is similar tothe Haldane model (36), in which a valley-contrasting mass term leads to opposite valleyshaving the same sign of the Berry curvature,leading to a nonzero total Chern number incrystalline graphene. Third, the Chern insula-tor in ABCA-4LG/WSe2 is at the charge-neutralpoint, which differs from the Chern insulatorsat certain fillings of Moiré superlattices. As aresult, the realization of a Chern insulator doesnot require precise control of the twist angle.Finally, theChernnumber of 4preciselymatchesthe winding number of ABCA-4LG, which im-plies an approach to developing a Chern in-sulator family with controllable Chern numbersby varying the layer number in thicker rhom-bohedral multilayer graphene with SOC.Our experiment showcases a system toachieve a Chern insulator state based on a tun-able LAF with SOC. Featuring highly tunablesymmetrieswithinone sample, including charge,spin, valley, layer, and SOC, ABCA-4LG/WSe2offers a flexible and versatile platform for fur-ther study. This simple structure also opens upavenues for investigating topological phasetransitions and potentially exploring topolog-ical phases such as topological superconductorsand fractional Chern insulators. 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Su, A. H. MacDonald, Phys. Rev. Lett. 125, 227702(2020).49. Y. Sha et al., Data for: Observation of Chern insulator incrystalline ABCA-tetralayer graphene with spin-orbit coupling,Dryad (2024); https://doi.org/10.5061/dryad.dncjsxm6d.ACKNOWLEDGMENTSWe thank F. Wu, Z. Qiao, J. Jung, W. Luo, and Y. Zhang for helpfuldiscussions. Funding: G.C. acknowledges support from NationalKey Research Program of China (grant nos. 2021YFA1400100 and2020YFA0309000), NSF of China (grant nos. 12350005 and12174248), SJTU (grant no. 21X010200846) and the YangyangDevelopment Fund. R.Z. acknowledges support from the Ministryof Science and Technology of China (grant nos. 2022YFA1402702and 2021YFA1401600) and NSF of China (grant nos. 12334008and 12374148). Z.S. acknowledges support from the National KeyResearch Program of China (grant no. 2021YFA1202902) andNSF of China (grant nos. 12074244 and 12374292). J.J.acknowledges support from the Ministry of Science andTechnology of China (grant no. 2019YFA0308600). K.W. andT.T. acknowledge support from the Japan Society for thePromotion of Science (JSPS) (KAKENHI grant nos. 20H00354,21H05233, and 23H02052) and the World Premier InternationalResearch Center Initiative (WPI), MEXT, Japan. Authorcontributions: G.C. conceived and supervised the project. Y.S.and K.L. fabricated the devices with and without WSe2,respectively. Y.S., J.Z., and K.L. performed the transportmeasurements. J.Z. set up the dilution refrigerator. H.D. and R.Z.grew the WSe2 bulk crystals. K.W. and T.T. grew the hBN bulkcrystals. Y.S., J.Z., K.L., and G.C. analyzed the data. Y.S. andG.C. wrote the paper with input from all authors. Competinginterests: The authors declare no competing interests. Data andmaterials availability: The data from this study are available atDryad (49).6 of 6https://doi.org/10.5061/dryad.dncjsxm6dhttps://www.science.org/about/science-licenses-journal-article-reusehttps://www.science.org/about/science-licenses-journal-article-reusehttps://science.org/doi/10.1126/science.adj8272