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Rui Chen, Fanhao Meng, Hongrui Zhang, Yuzi Liu, Shancheng Yan, Xilong Xu, Linghan Zhu, Jiazhen Chen, Tao Zhou, Jingcheng Zhou, Fuyi Yang, Penghong Ci, Xiaoxi Huang, Xianzhe Chen, Tiancheng Zhang, Yuhang Cai, Kaichen Dong, Yin Liu, [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), Chia-Ching Lin, Ashish Verma Penumatcha, Ian Young, Emory Chan, Junqiao Wu, Li Yang, Ramamoorthy Ramesh, Jie Yao

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[Room-temperature multiferroicity in sliding van der Waals semiconductors with sub-0.3 V switching](https://mdr.nims.go.jp/datasets/7b7258c8-5eae-4bba-9fe7-d19283c9823f)

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Room-temperature multiferroicity in sliding van der Waals semiconductors with sub-0.3 V switchingArticle https://doi.org/10.1038/s41467-025-58009-9Room-temperature multiferroicity in slidingvanderWaals semiconductorswith sub-0.3VswitchingRui Chen1,2,12, Fanhao Meng 1,2,12 , Hongrui Zhang 1,3,12, Yuzi Liu 4,12,Shancheng Yan 5,12, Xilong Xu6, Linghan Zhu 6, Jiazhen Chen1,2, Tao Zhou 4,Jingcheng Zhou1, Fuyi Yang1,2, Penghong Ci 1,2, Xiaoxi Huang 1,Xianzhe Chen1,2, Tiancheng Zhang 1, Yuhang Cai 1,2, Kaichen Dong1,2,Yin Liu 7, Kenji Watanabe 8, Takashi Taniguchi 8, Chia-Ching Lin9,Ashish Verma Penumatcha 9, Ian Young 9, Emory Chan 10, Junqiao Wu 1,2,Li Yang6, Ramamoorthy Ramesh 1,2,11 & Jie Yao 1,2The search for van der Waals (vdW) multiferroic materials has been challen-ging but also holds great potential for the next-generation multifunctionalnanoelectronics. The group-IV monochalcogenide, with an anisotropic puck-ered structure and an intrinsic in-plane polarization at room temperature,manifests itself as a promising candidate with coupled ferroelectric and fer-roelastic order as the basis for multiferroic behavior. Unlike the intrinsiccentrosymmetric AB stacking, we demonstrate a multiferroic phase of tinselenide (SnSe), where the inversion symmetry breaking is maintained in AA-stacked multilayers over a wide range of thicknesses. We observe that aninterlayer-sliding-induced out-of-plane (OOP) ferroelectric polarization cou-ples with the in-plane (IP) one, making it possible to control out-of-planepolarization via in-plane electric field and vice versa. Notably, thickness scalingyields a sub-0.3 V ferroelectric switching, which promises future low-power-consumption applications. Furthermore, coexisting armchair- and zigzag-likestructural domains are imaged under electron microscopy, providing experi-mental evidence for the degenerate ferroelastic ground states theoreticallypredicted. Non-centrosymmetric SnSe, as thefirst layeredmultiferroic at roomtemperature, provides a novel platform not only to explore the interactionsbetween elementary excitations with controlled symmetries, but also to effi-ciently tune the device performance via external electric and mechanicalstress.The emerging ferroic orders in 2D vdW materials have spurred inten-sive research interest from both fundamental physics and deviceapplication perspectives1–10. Multiferroic materials, possessing multi-ple collective state switches such as ferroelectricity, ferromagnetism,ferroelasticity and ferrotoroidicity, allow for the implementation ofcorrelated-electron systems into state-of-the-art devices, showingtremendous potential for attojoule logic computing and memory11–14.In the community of multiferroics, 2D vdW materials have gainedparticular attention owing to their ideal interfaces, fundamentally newphysics, miniaturized device footprint, flexibility of fabrication, toReceived: 29 August 2024Accepted: 10 March 2025Check for updatesA full list of affiliations appears at the end of the paper. e-mail: fhmeng@berkeley.edu; yaojie@berkeley.eduNature Communications |         (2025) 16:3648 11234567890():,;1234567890():,;http://orcid.org/0000-0002-3058-1542http://orcid.org/0000-0002-3058-1542http://orcid.org/0000-0002-3058-1542http://orcid.org/0000-0002-3058-1542http://orcid.org/0000-0002-3058-1542http://orcid.org/0000-0001-7896-019Xhttp://orcid.org/0000-0001-7896-019Xhttp://orcid.org/0000-0001-7896-019Xhttp://orcid.org/0000-0001-7896-019Xhttp://orcid.org/0000-0001-7896-019Xhttp://orcid.org/0000-0002-8733-1683http://orcid.org/0000-0002-8733-1683http://orcid.org/0000-0002-8733-1683http://orcid.org/0000-0002-8733-1683http://orcid.org/0000-0002-8733-1683http://orcid.org/0000-0003-2574-3479http://orcid.org/0000-0003-2574-3479http://orcid.org/0000-0003-2574-3479http://orcid.org/0000-0003-2574-3479http://orcid.org/0000-0003-2574-3479http://orcid.org/0000-0002-9259-5077http://orcid.org/0000-0002-9259-5077http://orcid.org/0000-0002-9259-5077http://orcid.org/0000-0002-9259-5077http://orcid.org/0000-0002-9259-5077http://orcid.org/0000-0002-8093-7666http://orcid.org/0000-0002-8093-7666http://orcid.org/0000-0002-8093-7666http://orcid.org/0000-0002-8093-7666http://orcid.org/0000-0002-8093-7666http://orcid.org/0000-0001-5949-6854http://orcid.org/0000-0001-5949-6854http://orcid.org/0000-0001-5949-6854http://orcid.org/0000-0001-5949-6854http://orcid.org/0000-0001-5949-6854http://orcid.org/0000-0002-8557-6791http://orcid.org/0000-0002-8557-6791http://orcid.org/0000-0002-8557-6791http://orcid.org/0000-0002-8557-6791http://orcid.org/0000-0002-8557-6791http://orcid.org/0009-0000-6538-3450http://orcid.org/0009-0000-6538-3450http://orcid.org/0009-0000-6538-3450http://orcid.org/0009-0000-6538-3450http://orcid.org/0009-0000-6538-3450http://orcid.org/0000-0002-6278-204Xhttp://orcid.org/0000-0002-6278-204Xhttp://orcid.org/0000-0002-6278-204Xhttp://orcid.org/0000-0002-6278-204Xhttp://orcid.org/0000-0002-6278-204Xhttp://orcid.org/0000-0002-5234-6922http://orcid.org/0000-0002-5234-6922http://orcid.org/0000-0002-5234-6922http://orcid.org/0000-0002-5234-6922http://orcid.org/0000-0002-5234-6922http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0003-3701-8119http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-1467-3105http://orcid.org/0000-0002-0329-3721http://orcid.org/0000-0002-0329-3721http://orcid.org/0000-0002-0329-3721http://orcid.org/0000-0002-0329-3721http://orcid.org/0000-0002-0329-3721http://orcid.org/0000-0002-4017-5265http://orcid.org/0000-0002-4017-5265http://orcid.org/0000-0002-4017-5265http://orcid.org/0000-0002-4017-5265http://orcid.org/0000-0002-4017-5265http://orcid.org/0000-0002-5655-0146http://orcid.org/0000-0002-5655-0146http://orcid.org/0000-0002-5655-0146http://orcid.org/0000-0002-5655-0146http://orcid.org/0000-0002-5655-0146http://orcid.org/0000-0002-1498-0148http://orcid.org/0000-0002-1498-0148http://orcid.org/0000-0002-1498-0148http://orcid.org/0000-0002-1498-0148http://orcid.org/0000-0002-1498-0148http://orcid.org/0000-0003-0524-1332http://orcid.org/0000-0003-0524-1332http://orcid.org/0000-0003-0524-1332http://orcid.org/0000-0003-0524-1332http://orcid.org/0000-0003-0524-1332http://orcid.org/0000-0003-0557-759Xhttp://orcid.org/0000-0003-0557-759Xhttp://orcid.org/0000-0003-0557-759Xhttp://orcid.org/0000-0003-0557-759Xhttp://orcid.org/0000-0003-0557-759Xhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-025-58009-9&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-025-58009-9&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-025-58009-9&domain=pdfhttp://crossmark.crossref.org/dialog/?doi=10.1038/s41467-025-58009-9&domain=pdfmailto:fhmeng@berkeley.edumailto:yaojie@berkeley.eduwww.nature.com/naturecommunicationsname a few. However, establishing two or more ferroic order para-meters especially at the 2D limit is faced with serious challenges, andso far experimental reports have been scarce. Recently,monolayer NiI2was experimentally demonstrated to be a type-II magnetoelectricmultiferroic system at cryogenic temperatures, bridging the gapbetween multiferroics and 2D materials15. In parallel to that, severalother 2D multiferroics are theoretically proposed16–20, which highlightnot only magnetoelectric coupling, but also potential association withferroelasticity.Layered group-IV monochalcogenides (MXs, M: Ge, Sn; X: S, Se)are orthorhombically distorted from the cubic structure, which yieldsextraordinary crystal anisotropy similar to phosphorene, and thusfascinating unconventional optical and thermoelectric properties21–27.MXs have been proposed to be a promising multiferroic system,potentially hosting both ferroelectricity in the monolayer and ferroe-lasticity in the bulk19,20. There are four energetically degenerate mul-tiferroic ground states, which results from the spontaneous tensilestrain along x and y relative to the cubic paraelectric (paraelastic)structure. Figure 1d depicts the free energy landscape as a function oflattice distortion εx (εy). The electric field E±x (E±y) drives the ferro-electric switching along x (y), whereas the mechanical stress σx (σy)leads to the ferroelastic transition into the x (y) axis. As a consequence,charge and lattice degrees of freedom inMXs are cross-linked throughthe four degenerate ground states, and with the non-volatile switchingby external fields, novel designs of functional devices utilizing theswitching of electric polarization and lattice strain can be achieved19,20.Experimentally, in-plane (IP) ferroelectricity was reported inmonolayer and AA-stacked few-layer MX, where imaging and manip-ulation of the ferroelectric domains was also demonstrated28–33. How-ever, OOP electric polarization which facilitates wider deviceapplications, remains elusive in this system. In particular, the richvariety of stacking symmetry and interlayer sliding configurations insuch vdW materials potentially offers a pathway to realize additionaldimensions of polarization7–10,34–38. In this work, we report the dis-covery of the non-centrosymmetric stacking and interlayer slidingwhich give rise to co-existing and correlated IP and OOP ferroelectricproperties. Such ferroelectrically stacked vdW layers offer a nearlylinear scaling behavior, i.e., as the material thickness scales down, theferroelectric switching voltage of SnSe reaches sub-0.3 V, which offersnew opportunity towards future attojoule energy-efficientapplications28–31. In addition, we also observe two types of character-istic ferroelastic domains in such SnSe nanosheets with HRTEM fromthe same cross section. For the first time, we experimentally demon-strate the coexistence of ferroelectric and ferroelastic orders in a 2DvdW system. The extension of 2D multiferroic family to room tem-perature will bring about more in-depth explorations of intrinsiccoupling between ferroic orders. In contrast with previous reports onMXs29,30,32,33,39, our work on the AA-stacked SnSe not only relaxes thestringent thickness limitation towards ferroelectricity but alsoexperimentally demonstrates the existence of multiferroic order.Multiferroic SnSe with OOP polarization unlocks abundant degrees offreedom to tune the material figures of merit for low-power deviceapplications, such as non-volatile memory, logic, photodetector,actuator, and so forth11,40–44.ResultsAA-stacking and broken inversion symmetryWe realize a low-temperature (250 °C) physical vapor deposition (PVD)growth of AA-stacked (more evidence in Fig. 3) SnSe single crystals ona variety of substrates, including silicon (“Methods”). This low-temperature recipe allows for high compatibility with the back-end-of-line (BEOL) of complementary metal-oxide-semiconductor (CMOS)technologies. Opticalmicroscope images of SnSe flakes onSi substrateare presented in the Supplementary Fig. S1. The thickness of as-grownSnSe varies from 5 nm to a few microns, with slight adjustment of thegrowth condition as discussed in “Methods” section. Mechanicalexfoliation also assists in thinning down the nanoflakes. Figure 1ashows the crystal structureof theAA-stackingphase of SnSe,where thelateral orientation of each layer is aligned (Fig. 1b). In contrast tocentrosymmetric AB-SnSe (Fig. 1c), AA-stackingpreserves theC2v pointgroup as of the monolayer, realizing a non-centrosymmetric phasewith thickness ranging up to over 100nm as we have tested.In order to study the symmetry of synthesized crystals, we firstconduct optical second harmonic generation (SHG) measurements(“Methods”)45–47. An 800nm pulsed laser is incident normal to thesample plane, and the linear polarizer and analyzer are maintainedparallel to each other. Strong SHG signals at 400nm wavelength areobserved, with the second-order nature confirmed by the power-dependent measurement as plotted in Supplementary Fig. S2b45. ThestrongSHGresponse confirms thebroken inversion symmetryof the as-grown SnSe crystals, in contrast to the conventional AB-SnSe withvanishing SHG. A pair of half-wave plates placed in the incidence anddetection path respectively, are rotated together to obtain thepolarization-dependent SHG. An angular pattern corresponding to theC2vpoint groupwas clearly revealed, as shown inFig. 1e. Togain insightsinto the stacking symmetry, we calculated the second-order nonlinearsusceptibility of bilayer AA-SnSe (Fig. 1f, “Methods”), with the in-planeSHG response written as: χk =�2χxxy + χyxx�sinθcos2θ+ χyyysin3θ. Asdisplayed in Fig. 1e, the experimental data agree well with the calcula-tion results, suggesting theAA stacking of our synthesized SnSe crystalswith a broken inversion symmetry. Such consistency was further ver-ified by the polarization-dependent SHG pattern at 1064nm CW laserexcitation, as shown in Supplementary Fig. S2c,d.IP and OOP ferroelectricity with low-voltage switchingTo verify the spontaneous polarization in the non-centrosymmetricSnSe, we investigated the ferroelectric behavior through the Dual ACResonance Tracking (DART) piezoresponse force microscopy (PFM,see “Methods”). Figure 2a presents a schematic illustration of in-planePFMmeasurements. A DC voltage is applied between the tip andmetalelectrode, so that the horizontal electric field can switch the IP electricpolarization30. In the meantime, an AC voltage is used to detect thepiezoelectric response which is associated with the electric polariza-tion. As shown in Fig. 2b, the typical butterfly-shaped amplitudebehavior and the hysteretic phase against bias curve indicate the in-plane ferroelectricity in the SnSe sample. Such behaviors have beenobserved in all samples we have tested, with various thicknesses.Notably, previous attempts to identify ferroelectricity in MXs wereonly limited in monolayer or few layers, mainly due to the loss of AA-stacking in thicker samples29. Our synthesized SnSe, as a new polarcrystal, overcomes such thickness restriction and show consistentferroelectric response at all thicknesses.In themeantime, we also observe the OOP ferroelectric responsesin our SnSe crystals, which was not discussed in previous theoreticalproposals. Furthermore, as the vertical electrical response has anintrinsic connection with the thickness of the samples, particularattention has been paid to identifying low switching voltage of SnSe,from the perspective of low-power device applications. As shown inFig. 2c, the vertical electric field between the tip and heavily dopedsilicon substrate can flip the OOP polarization in SnSe. Figure 2d dis-plays the representative hysteresis loops of phase and butterfly-shaped amplitude as a function of bias, indicative of the OOP ferroe-lectricity. The thickness of this sample is 87.1 nm, and the corre-sponding coercive voltage is around 2.1 V.In light of the thickness dependence of the OOP ferroelectricswitching voltage, we then explore the SnSe sheets with reducedthicknesses. By increasing the carrier gas flow and decreasing both thegrowth temperature and growth time, we were able to suppress thelayer-by-layer growth, and thus, to substantially decrease the thicknessof SnSe sheets down to nanometer scale. It is worth noting that theArticle https://doi.org/10.1038/s41467-025-58009-9Nature Communications |         (2025) 16:3648 2www.nature.com/naturecommunicationscoercive voltage is only 0.28 V when the thickness reaches 5 nm(Fig. 2e), which is remarkably lower than that of hafnium oxides48 andother 2D ferroelectrics5–10. Figure 2f summarizes the reduction ofswitching voltage as the sample thickness decreases. It shows a cleartrend that the coercive voltage scales almost linearly with samplethickness. It has been reported that the depolarization field in ultrathinarmchairSnSea bcdfeABAAFig. 1 | Crystal structure and non-centrosymmetric stacking of SnSe.a Schematic crystal structure of non-centrosymmetric SnSe displaying an AA-typestacking, where every single layer is vertically aligned. Blue and yellow spheresrepresent Sn and Se atoms, respectively. b, c Schematic illustration of bilayer SnSewith AA and AB stacking symmetry. For centrosymmetric AB stacking, adjacentlayers are antiparallel to each other. d Schematic of the multiferroic ground statespredicted inMXs. The landscape of Landau free energy illustrates four ferroelectric(ferroelastic) states, P±x and P±y, in the xy plane. Non-volatile ferroelectric phasetransition along x (y) can be triggered by the E-field E±x (E±y) along x (y).Meanwhile,the stress σx (σy) along x (y) drives the ferroelastic states from Py (Px) into Px (Py),which is also non-volatile. In that sense, electric field control of ferroelasticity andstress control of ferroelectricity are enabled in multiferroic MXs. e Polarization-dependent in-plane SHG of synthesized SnSe, consistent with the ab initio calcu-lations of bilayer AA-SnSe (red curve). The polarizer and the analyzer are set to beparallel to each other. f DFT calculation of the in-plane second-order susceptibilityresponse of bilayer AA-SnSe.Article https://doi.org/10.1038/s41467-025-58009-9Nature Communications |         (2025) 16:3648 3www.nature.com/naturecommunicationsferroelectric films may suppress the coercive field49. This may deviatethe system from the classical Janovec-Kay-Dunn (JKD) scaling, andinduce the essentially thickness-independent coercive field. The linearfitting shows a slope of about 200 kV/cm, which agree with the nearlyconstant coercive field in samples above 35 nm (SupplementaryFig. S6). As the material further thins down, more reduction of theswitching voltage is expected, although the measured coercive fieldtends to increase, which might pose a limit to the smallest switchingvoltage we can achieve. Future efforts including interface engineering,defect engineering and doping engineering could potentially lead toultralow voltage switching in fewer layer SnSe nanosheets. Driving thelower limit of ferroelectric operation voltagewill open up new avenuestowards next-generation non-volatile nanoelectronic devices withultra-low power consumption11,41,50.Sliding induced OOP polarization and its coupling mechanismHaving verified the ferroelectricity in SnSe, we then analyze theunderlying mechanisms through a combination of high-resolutionTEM (HRTEM) and density functional theory (DFT) calculations(“Methods”). Figure 3a presents the cross-sectional TEM image withelectron beam along [010] zone axis. The HRTEM image clearly showsthe vertically aligned armchair-like structure and matches very wellwith the AA stacking model. It confirms that our as-grown SnSe flakesare AA stacked with accumulated polarization, in stark contrast withconventional MXs with centrosymmetric AB stacking and thus nospontaneous polarization25,51. In order to further prove the AA stackingorder, we conducted selected area electron diffraction (SAED) alongthe [010] zone axis and compared it with simulations (“Methods”). Theexperimental pattern (Fig. 3b) displays the orthorhombic symmetryand high crystalline quality, and more importantly, matches well withthe simulated pattern of AA-SnSe (Fig. 3c), while ruling out AB stacking(Supplementary Fig. S7). Therefore, we unambiguouslyunravel theAA-stacking of SnSe with inversion symmetry breaking, which is anessential prerequisite for the existence of ferroelectricity. It should beemphasized that this is the first time an AA stacking phase stabilized inbulk MXs is observed.As aforementioned, the superposition of monolayer polarizationwith AA-stacking would enable the IP ferroelectric order in multilayerSnSe. While for the OOP dipole, we show in the following that theinterlayer sliding plays a dominant role, in analogy to the “sliding fer-roelectricity” in other 2D materials7,9,10,34–36,52–54. Through analyzing theindividual atomic positions and shifts in the TEM image, we are able toobserve a collective interlayer sliding (Fig. 3d, e and SupplementaryFig. S9). The overall shift of Sn2+ and Se2− ions between adjacent layersgives rise to unbalanced interlayer dipoles, resulting in a non-zero netOOP polarization (Fig. 4a). The direction of OOP polarization isdetermined by the sliding direction and locked to the IP polarizationstate, thus accounts for the observed OOP ferroelectricity. With aleftward sliding as in Fig. 4a, when the IP state is switched from +PIP to−PIP, the OOP dipoles flip from −POOP to +POOP correspondingly, andvice versa. Such coupling arises as a direct consequence of AA stackingand sliding structure, as the (−POOP, +PIP) and (+POOP, −PIP) groundstates are intrinsically associatedwith a C2y symmetry operation in thisfashion (Supplementary Fig. S10).To further understand the sliding induced OOP polarization andthe coupled switching process, we perform first-principles DFT cal-culations of a bilayer AA-SnSe structure. By varying the interlayer shiftwhile relaxing the atomic structures, we observe a double-well-shapedprofile of the total energy (Fig. 4b). Two local energy minima with anopposite OOP polarization are identified aside the energy maximum(corresponding to the non-polarized intermediate state), and the sys-tem tends to relax into either of these energy-favorable states, agree-ing well with the experimentally observed collective sliding structure.Following the ferroelectric switching process depicted in Fig. 4a withead fbcGNDPtVDC+ACSiO2SiVDC+ACSi GNDFig. 2 | IP andOOP ferroelectric switching verified by PFM. a Schematic of the IPPFMmeasurements. SnSenanoflakes are preparedon the300nmSiO2/Si substrate.A Pt electrode is fabricated grounding one side of the SnSe sample. An IP electricfield is applied between the electrode and tip for the switching and probe of localpolarization. (GND: ground)b IP PFMphase and amplitude as a function of voltage.Non-volatile IP ferroelectricity is evidenced by the hysteresis recorded in “DC off”mode. The sample thickness is 81.6 nm. c Schematic of OOP PFM measurements.SnSe nanoflakes are grown on a heavily doped Si substrate, which serves as thebottom electrode. The biased tip that contacts the sample senses the OOP piezo-electric response.dOOPPFMphase and amplitude (“DCoff”mode) as a function ofvoltage. Similar to the IP results in (b), the hysteretic switching behaviors explicitlyindicate the non-volatile bulk ferroelectricity along the OOP direction. The samplethickness is 87.1 nm. e OOP PFM results of 5-nm-thick SnSe sheet exhibiting a lowswitching voltage of 0.28V. The arrows in figure denote the sweeping directions ofvoltage. f Evolution of switching voltage as sample thickness scales down. Analmost linear relationship is indicated by the red line.Article https://doi.org/10.1038/s41467-025-58009-9Nature Communications |         (2025) 16:3648 4www.nature.com/naturecommunicationsthe lowest-energy amount of interlayer sliding, both the IP and OOPpolarization values are calculated along the ferroelectric switchingpath using the nudged elastic band (NEB) method (Fig. 4c), whichreveals a coupled switching behavior, where the IP polarization andOOPpolarization changes synchronously. The correlation between theIP and OOP switching is further supported by the modulation of IPoptical SHG using an OOP E-field (Supplementary Fig. S12). Theemergence of such an interlocked mechanism will provide extra tun-ability for future state-of-the-art device applications based on SnSe orsimilar ferroelectrics.Ferroelastic domain imagingIn addition to ferroelectricity, ferroelasticity also attracts concertedresearch interest and it has long been predicted in the MX family19,20.However, experimental demonstration of ferroelastic MXs is lacking,mainly due to technical challenges. HRTEM can detect the atomicdisplacement with a resolution of 0.5 Å55. Consequently, it is regardedas an optimal technique to directly image the ferroelastic domains.Pioneering theories pointed out that two characteristic ferroelasticdomains, (100) and (010), coexist in SnSe nanosheets, and the fer-roelastic phase transition occurswhen themechanical stress is appliedFig. 4 | The coupled IP and OOP ferroelectric switching mechanism in SnSe.a Schematic illustration of the ferroelectric switching with coupled IP and OOPdipoles. The net IP ferroelectric polarization accumulates from the AA stackedlayers. OOP ferroelectric polarization forms due to the sliding-induced misalign-ment of charged ions (Sn2+ and Se2−) from neighboring layers. The dominant dipoleis denoted by the dashed ovals. When the IP ferroelectric configuration is switched(blue arrow), the OOP polarization (red arrow) switches simultaneously, and viceversa. b Calculated energy profile associated with the interlayer sliding (shift),showing a double-well-like behavior. c Calculated net OOP and IP polarization (perunit cell) along the ferroelectric switching path (λ is the relative NEB coordinate).The OOP and IP polarizations are switched simultaneously resulting from theinterlayer sliding configuration. The inset denotes the ferroelectric ground statesand intermediate state as illustrated in (a).ca b2 nmd eFig. 3 | TEM evidence of the AA stacking and interlayer sliding in SnSe. a The(010) crystal plane of synthesized SnSe imaged by HRTEM. Heavier Sn atoms arebrighter while the lighter Se atoms are slightly darker. A schematic crystal model ofAA-stacked SnSe (inset) can fit well with our experimental data. The top amorphousregion corresponds to the metal deposited during the cross section preparationprocess. SAED (selected area electron diffraction) patterns of SnSe along the [010]zone axis through the experiments of synthesized SnSe (b) and the simulations ofbulk AA-SnSe (c). The perfect consistency between experiments and simulationsfurther verifies the AA-stacking symmetry. d Analysis of the atomic positions fromthe side view imaged by HRTEM. Atoms are classified into four types in terms oftheir positions within the unit cell, marked by orange, red, green and blue spheres,respectively. e The horizontal position of atoms from different layer numbers. Theerror bars indicate the variance of individual atoms’ horizontal positionwithin eachlayer. A collective interlayer sliding is explicitly observed. From the linear fitting,the average atomic sliding is 0.052 ± 0.002, 0.039± 0.005, 0.050 ±0.003,0.037 ± 0.003Å, respectively.Article https://doi.org/10.1038/s41467-025-58009-9Nature Communications |         (2025) 16:3648 5www.nature.com/naturecommunicationsalong xor y crystal orientation19,20 (Fig. 1d). Such stress distributionandthe formation of ferroelastic domains is most evident from cross-sectional TEM images. Froma low-magnification side view (Fig. 5a), thestark contrast in the image exhibits alternating bright and dark stripes-like patterns suggesting a non-uniform strain distribution, which istypical of ferroelastic materials56,57. With a higher-magnification imagetaken around the domainwall (Fig. 5b and Supplementary Fig. S13), wecan clearly reveal the coexistence of (100) (green box) and (010)(yellow box) domains on the same cross section. The inset within theyellow (green) box schematically shows the fitting of Sn and Se posi-tions, corresponding to an armchair (zigzag) type of structure. Notethat the notation of armchair and zigzag here follows the conventionused in previous anisotropic Raman studies58, and is characteristic forthe (010) and (100) planes of the puckered SnSe structure. We alsoutilize polarized Raman measurements from the top surface to dis-tinguish the anisotropy between these two types of domains, and theresults are summarized in Supplementary Fig. S14. Even higher-magnification images inside the yellow/green boxes are shown inFig. 5c, d, confirming the good agreement of two types of ferroelasticdomains, unambiguously proving the coexistence of two ferroelasticground states in SnSe.In summary, we experimentally report the coexisting ferroelec-tricity and ferroelasticity in MXs. Low-temperature (250 °C) synthesisof SnSe is highly amenable to the BEOL of semiconductor manu-facturing process. We observed for the first time the interlayer slidingenabled OOP polarizations in MX systems. Correlated IP and OOPferroelectric switching is identified in SnSe due to the unique stackingconfiguration. The switching voltage exhibits a nearly linear scalingwith respect to the sample thickness, decreasing to as lowas0.28 V in a5-nm-thick sheet. The addition of ferroelastic to MXs greatly enhancesthe tunability of ferroelectric properties potentially by strain engi-neering. The discovery of multiferroic behavior in layered SnSe pre-sents an exciting landmark in the innovation of low-power and highlytunable memory40 and logic devices11,41.MethodsMaterial synthesisAA-stacking SnSe single crystals are directly synthesized on silicon bythe low-temperature PVD method. Commercialized SnSe powders(99.999% metals basis, Sigma-Aldrich) are used as the source and amixture of Ar/H2 gas is chosen as the carrier gas. Typical growthconditions utilize low pressure of 60mTorr and flow rate of 60 stan-dard cubic centimeters per minute (sccm). The source temperature atthe center of the tube furnace is set to600–650 °C, and the evaporatedSnSe is deposited downstreamonto the substrate at a low temperatureof 250 °C. To favor the formation of thinner flakes, the center tem-perature is reduced to 550–600 °C, with increased flow rate of100 sccm and pressure of 150mTorr, along with reduced growth time.The typical lateral size for 5–10 nm thick flakes is 5–10μm, and10–20μm for relatively thicker flakes. The uniformity and yield of theAA-stacking phase are verified by HRTEM and electron diffractionacross multiple samples.SHG measurements and calculationsOptical SHG signals of SnSe nanoflakes are measured under both800nm femtosecond laser (main text) and 1064nm CW laser (Sup-plementary Information) excitation. The 800nm fs measurements areperformed in a home-built setup using a Ti:sapphire laser (CoherentChameleon Ultra II, 140 fs, 80MHz), focused onto a 1–2μmspot with a50x objective lens. The polarization state was established with a linearpolarizer and half-wave plate, while the second harmonic beam waspicked by a shortpass filter and analyzed by another half-wave plateand linear polarizer. CW 1064 nmmeasurements are performed usinga Horiba Jobin Yvon LabRAM ARAMIS confocal Raman microscope.The linear polarizer and analyzer are parallel/orthogonal to each otherwhile the samples are rotated to probe the polarization dependence.The CW laser (Laser Quantum Ventus 1064) is focused onto a ~1μmspot with a 100x objective. The calculation of angle-dependent SHGspectra is obtained using the ArchNLO package based on the pertur-bation theory of polarization operator. A dense k-grid of 27 × 27 × 1,and the inclusion of 200 conduction bands are used to get the con-verged optical susceptibilities.PFM measurementsDRAT PFM (MFP-3D, Asylum Research) is employed to explore theferroelectric switching of SnSe in both horizontal and vertical modes.A metallic Pt-coated cantilever (MikroMasch HQ: NSC18/PT) is used todetect the local piezoelectric deformation of sample. Under the hor-izontal mode, the electric field forms between the tip and side elec-trode. As for the vertical mode, the electric field lies between the tipand bottom p+ Si substrate. The data was recorded in the non-volatile“DC off” mode, while the “DC on” data is shown in SupplementaryFig. S4 for comparison.TEM characterizationBoth the top and side view of SnSe nanoflakes are captured by HRTEM.Top-view SnSe nanoflakes are directly transferred onto commercializedTEMgrids via dry transfermethod. The side-view samples are fabricatedby focused ion beam (FIB). At the end of FIB process, 5 kVGa ion beam isutilized to remove the damage of samples by 30 kV Ga ion beams. Afterthe delicate sample fabrication, the HRTEM images and electron dif-fraction patterns are taken by using a FEI Titan operated at 200kV andequipped with an image Spherical Aberration Corrector at 200kV.First-principles calculationsThe ground-state structural and electronic properties of bilayer SnSeare calculated by DFT within the generalized gradient approximation(GGA) using the Perdew-Burke-Ernzerhof (PBE) functional, as imple-mented in the Vienna ab initio simulation package (VASP). A k-pointsampling of 12 × 12 × 1 and a plane-wave basis with an energy cutoff ofacbd200 nm2 nmFig. 5 | Two types of ferroelastic domains imaged by HRTEM. a Low-magnification cross-sectional TEM of SnSe. The stripes-like contrast variationindicates the presence of strain which is typically associated with ferroelasticdomains. b Side-view HRTEM image under a higher magnification. A typical (010)type (armchair) configuration is shown in the yellow box and (100) type (zigzag)configuration is shown in the green box. The white dashed line indicates thedomain boundary. c, d Zoom-in images of the atomic arrangements inside the twodomains, showing good agreement with the (010) and (100) crystal plane.Article https://doi.org/10.1038/s41467-025-58009-9Nature Communications |         (2025) 16:3648 6www.nature.com/naturecommunications450eV is employed to obtain the converged charge densities andwavefunctions. The vdW interactions are included via the semi-empirical Grimme-D3 scheme with zero-damping. A vacuum distanceof 18 Å between adjacent layers is used along the periodic direction toavoid spurious interactions. Spin orbit coupling (SOC) is included. Theenergy barrier of the ferroelectric phase transition from negative topositive OOP polarized configuration is calculated by the nudgedelastic band (NEB) method.Reporting summaryFurther information on research design is available in the NaturePortfolio Reporting Summary linked to this article.Data availabilityRelevant data generated in this study are provided in the article andSupplementary Information. All raw data that support the plots withinthis paper and other findings of this study are available from the cor-responding authors upon request.References1. Zhang, D., Schoenherr, P., Sharma, P. & Seidel, J. Ferroelectricorder in van der Waals layered materials. Nat. Rev. Mater. 8,25–40 (2023).2. Wu,M. Two-dimensional vanderWaals ferroelectrics: scientific andtechnological opportunities. ACS Nano 15, 9229–9237 (2021).3. Burch, K. S., Mandrus, D. & Park, J.-G. Magnetism in two-dimensional van der Waals materials. Nature 563, 47 (2018).4. Gong, C. & Zhang, X. 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R.R. acknowledges theAir Force Office of Scientific Research 2D Materials and DevicesResearch program through Clarkson Aerospace Corp under Grant No.FA9550-21-1-0460. X.H. is supported by the SRC-ASCENT center whichis part of the SRC-JUMP program. Use of the Center for NanoscaleMaterials, an Office of Science user facility, was supported by the U.S.Department of Energy, Office of Science, Office of Basic Energy Sci-ences, under Contract No. DE-AC02-06CH11357. Work at the MolecularFoundry was supported by the Office of Science, Office of Basic EnergySciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. The devices were fabricated in the UC Berkeley MarvellNanofabrication Laboratory. We acknowledge the Biomolecular Nano-technology Center for access and assistance with measurementsystems.Author contributionsR.C., F.M. and J.Y. conceived the project and designed the experiments.R.C. performed the PFM measurements. Y.Z.L., T.Z., R.C., F.M. and Y.L.conducted the TEM characterizations and analyses. X.X., L.Z. and L.Y.carried the theoretical calculations. F.M., R.C., J.C., F.Y. and E.C.obtained the optical data. R.C., J.C., S.Y. and J.Z. synthesized the sam-ples. R.C., S.Y., H.Z., X.H., X.C., T.C.Z., Y.C. and K.D. fabricated thedevices. R.C., F.M., H.Z., P.C. and Y.C. performed electrical measure-ments under the supervision of J.W. K.W. and T.T. grew the hBN crystal.C.-C.L., A.V.P., I.Y. and R.R. contributed to the data analysis. R.C., F.M.and J.Y. wrote the manuscript. All authors discussed the results andcommented on the manuscript.Competing interestsThe authors declare no competing interests.Additional informationSupplementary information The online version containssupplementary material available athttps://doi.org/10.1038/s41467-025-58009-9.Correspondence and requests for materials should be addressed toFanhao Meng or Jie Yao.Peer review information Nature Communications thanks Xiaobao Tian,William Wilson, and the other, anonymous, reviewer(s) for their con-tribution to the peer review of this work. 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To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.© The Author(s) 20251Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA. 2Materials Sciences Division, Lawrence BerkeleyNational Lab, Berkeley, CA 94720, USA. 3Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, China.4Center forNanoscaleMaterials, Nanoscience andTechnologyDivision, ArgonneNational Laboratory, Lemont, IL60439,USA. 5Collegeof Industry-EducationIntegration, Nanjing University of Posts and Telecommunications, Nanjing 210023, China. 6Department of Physics and Institute of Materials Science andEngineering,WashingtonUniversity inSt. Louis, St. Louis,MO63130,USA. 7Department ofMaterials Science andEngineering, NorthCarolinaStateUniversity,Raleigh, NC 27606, USA. 8National Institute for Material Science, Tsukuba 305-0047, Japan. 9Components Research, Intel Corporation, Hillsboro, OR 97124,USA. 10The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 11Department of Physics, University of California, Berkeley,CA 94720, USA. 12These authors contributed equally: Rui Chen, Fanhao Meng, Hongrui Zhang, Yuzi Liu, Shancheng Yan. e-mail: fhmeng@berkeley.edu;yaojie@berkeley.eduArticle https://doi.org/10.1038/s41467-025-58009-9Nature Communications |         (2025) 16:3648 8https://doi.org/10.1038/s41467-025-58009-9http://www.nature.com/reprintshttp://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/mailto:fhmeng@berkeley.edumailto:yaojie@berkeley.eduwww.nature.com/naturecommunications Room-temperature multiferroicity in sliding van der Waals semiconductors with sub-0.3 V switching Results AA-stacking and broken inversion symmetry IP and OOP ferroelectricity with low-voltage switching Sliding induced OOP polarization and its coupling mechanism Ferroelastic domain imaging Methods Material synthesis SHG measurements and calculations PFM measurements TEM characterization First-principles calculations Reporting summary Data availability References Acknowledgements Author contributions Competing interests Additional information