Cu/Co, Cu/NiFe, Ta/NiFe bilayers and Co/Cu/Co, Co/Cu/NiFe, Co/Ta/NiFe sandwich films were deposited by a magnetron sputtering method. Magnetic properties were evaluated by VSM and spin valve magnetoresistance was inve...Cu/Co, Cu/NiFe, Ta/NiFe bilayers and Co/Cu/Co, Co/Cu/NiFe, Co/Ta/NiFe sandwich films were deposited by a magnetron sputtering method. Magnetic properties were evaluated by VSM and spin valve magnetoresistance was investigated by a four-probe method to study the interlayer coupling of the two magnetic layers. It has been found that the interlayer coupling depended not only on the layer thickness of the nonmagnetic spacer but also on the nature of the spacer. The interlayer coupling was reduced as the spacer layer thickness increased. The result was consistent with those from observations of the magnetic domain for the trilayers by means of Lorentz Electron Microscope. The trilayers with Cu spacer layer have shown a stronger coupling than those with Ta spacer layer.展开更多
Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Her...Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Here,we study modulations of the electronic structure induced by the interlayer coupling in theγ-phase of indium selenide(γ-InSe)using scanning probe techniques.We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction,which are attributed to strong interlayer coupling.In addition,the moirépatterns observed inγ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns.This suggests that modulation of the electronic structure induced by the moirépotential is smeared out,indicating the presence of a significant interlayer coupling.Our theoretical calculations confirm that the interlayer coupling inγ-InSe is not only of the van der Waals origin,but also exhibits some degree of hybridization between the layers.Strong interlayer coupling might play an important role in the performance ofγ-InSe-based devices.展开更多
Fe-Si/Cr multilayers with amorphous Fe-Si magnetic layers and Cr nonmagnetic layers were prepared by an rf-sputtering method.When the thickness of the Cr layers varies from 0.5 to 6 nm, the interlayer coupling oscilla...Fe-Si/Cr multilayers with amorphous Fe-Si magnetic layers and Cr nonmagnetic layers were prepared by an rf-sputtering method.When the thickness of the Cr layers varies from 0.5 to 6 nm, the interlayer coupling oscillates periodically from ferromagnetic to antiferromagnetism. For each sample only one wide uniform resonance peak is detected by the ferromagnetic resonance. The uniform resonance field Hb and the resonance line width △H_b oscillate periodically as the thickness of the Cr layers increases, which is related to the oscillation of the interlayer coupling from ferromagnetic to antiferromagnetism.The oscillation period is about 1.5nm.展开更多
Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal...Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique. The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.展开更多
The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) ...The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, Fe Co B/Ru/Fe Co B sandwich trilayers with Ru thickness(tRu) ranging from 1 A to 16 A are prepared by a compositional gradient sputtering(CGS) method. It is revealed that a stress-induced anisotropy is present in the Fe Co B films due to the B composition gradient in the samples. A tRu-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of 2 A ≤ tRu≤ 8 A and over 16 A, while an FM coupling is present in a range of tRu< 2 A and 9 A ≤ tRu≤ 14.5 A. It is interesting that an ultrahigh optical mode(OM) FMR frequency in excess of 20 GHz is obtained in the sample with tRu= 2.5 A under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of tRuare verified by Layadi’s rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.展开更多
The stacking structure of Nb_(2)CSe_(2),a newly synthesized layered metal carbo-selenide,was elucidated by scanning transmission electron microscopy.Nb,CSe2 features Se-Nb-C-Nb-Se quintuple atomic layers.These layers ...The stacking structure of Nb_(2)CSe_(2),a newly synthesized layered metal carbo-selenide,was elucidated by scanning transmission electron microscopy.Nb,CSe2 features Se-Nb-C-Nb-Se quintuple atomic layers.These layers are stacked in Bernal mode.In this mode,Nb,CSe2 crystallizes in a trigonal symmetry(space group P3m1,No.164),with lattice parameters of a=3.33 A and c=18.20 A.Electronic structure calculations indicate that the metal carbo-selenide has Fermi energy crossing the bands where it touches to give a zero gap,indicating that it is an electronic conductor.As evidenced experimentally,the electrical conductivity is as high as 6.6×10^(5) S·m^(-1),outperforming the counterparts in the MXene family.Owing to the layered structure,the bonding in Nb_(2)CSe_(2) with an ionic formula of(Nb^(1.48+)),(C^(1.74-))(Se^(0.61-))_(2) is highly anisotropic,with metallic-covalent-ionic bonding in intralayers and weak bonding between interlayers.The layered nature is further evidenced by elastic properties,interlayer energy,and friction coefficient determination.These characteristics indicate that Nb_(2)CSe_(2) is an analog of molybdenum disulfide(MoS_(2)),which is a typical binary van der Waals(vdW)solid.Moreover,vibrational properties are reported,which may offer an optical identification standardfor new ternary vdW solids in spectroscopic studies,including Raman scatteringand infrared absorption.展开更多
Interlayer exchange coupling(IEC)plays a critical role in spin-orbit torque(SOT)switching in synthetic magnets.This work establishes a fundamental correlation between IEC and SOT dynamics within Co/Pt-based synthetic ...Interlayer exchange coupling(IEC)plays a critical role in spin-orbit torque(SOT)switching in synthetic magnets.This work establishes a fundamental correlation between IEC and SOT dynamics within Co/Pt-based synthetic antiferromagnets and synthetic ferromagnets.The antiferromagnetic and ferromagnetic coupling states are precisely engineered through Ruderman-Kittel-Kasuya-Yosida(RKKY)interactions by modulating the Ir spacer thickness.Experimental results reveal that the critical switching current density exhibits a strong positive correlation with the IEC strength,regardless of the coupling type.A comprehensive theoretical framework based on the Landau-Lifshitz-Gilbert equation elucidates how IEC contributes to the effective energy barrier that must be overcome during SOT-induced magnetization switching.Significantly,the antiferromagnetically coupled samples demonstrate enhanced SOT efficiency,with the spin Hall angle being directly proportional to the antiferromagnetic exchange coupling field.These insights establish a coherent physical paradigm for understanding IEC-dependent SOT dynamics and provide strategic design principles for the development of energy-efficient next-generation spintronic devices.展开更多
The complex interplay of magnetic interactions at the yttrium iron garnet(YIG)/ferromagnet interface is important for spintronic and magnonic devices.In this study,we present a comprehensive investigation of the inter...The complex interplay of magnetic interactions at the yttrium iron garnet(YIG)/ferromagnet interface is important for spintronic and magnonic devices.In this study,we present a comprehensive investigation of the interlayer coupling and switching mechanisms in YIG/Py(permalloy)heterostructures based on gadolinium gallium garnet(GGG)and SiO_(2)substrates.We observe antiferromagnetic interlayer coupling between Py and YIG on SiO_(2)substrates,whereas ferromagnetic interlayer coupling is observed on GGG substrates.Using polarized neutron reflectometry with depth-and elementresolved measurements,we obtain an in-depth understanding of the magnetic interactions between the YIG and Py layers.We demonstrate that polycrystalline YIG gives rise to antiferromagnetic interlayer coupling.This work provides valuable insights into designing and controlling magnetic coupling in hybrid structures for spintronic applications.展开更多
Tungsten disulfide(WS_(2))has been reported to show negligible stacking dependence under ambient conditions,impeding its further explorations on physical properties and potential applications.Here,we realize efficient...Tungsten disulfide(WS_(2))has been reported to show negligible stacking dependence under ambient conditions,impeding its further explorations on physical properties and potential applications.Here,we realize efficient modulation of interlayer coupling in bilayer WS_(2)with 3R and 2H stackings by high pressure,and find that the pressure-triggered interlayer coupling and pressure-induced resonant-to-nonresonant transition exhibit prominent stacking dependence,which are experimentally observed for the first time in WS2.Our work may unleash the stacking degree of freedom in designing WS_(2)devices with tailored properties correlated to interlayer coupling.展开更多
Surface adsorption plays a crucial role in various natural and industrial processes,particularly in the field of energy storage.The adsorption of sodium atoms on 2D layered materials can significantly impact their per...Surface adsorption plays a crucial role in various natural and industrial processes,particularly in the field of energy storage.The adsorption of sodium atoms on 2D layered materials can significantly impact their performance as carriers and electrodes in ion batteries.While it is commonly acknowledged that pristine graphene is not favorable for sodium ion adsorption,the suitability of other 2D materials with similar honeycomb symmetry remains unclear.In this study,we employ systematic first-principles calculations to explore interlayer interactions and electron transfer effects on sodium adsorption on 2D van der Waals(vdW)heterostructures(HTSs)surfaces.Our results demonstrate that sodium adsorption is energetically favorable on these substrates.Moreover,we find that the adsorption strength can be effectively tuned by manipulation of the electron accumulation or depletion of the layer directly interacting with the sodium atom.By stacking these layered materials with different electron abundancy to form vd W HTSs,the charge density of the substrate becomes tunable through interlayer charge transfer.In these vdW HTSs,the adsorption behavior of sodium is primarily controlled by the absorption layer and exhibits a linear correlation with its pz-band center.Additionally,we identify linear correlations between the sodium adsorption energies,the electron loss of the sodium atom,the interlayer charge transfer,and the heights of the adsorbed sodium atom.These discoveries underscore the impact of interlayer electron transfer and interactions on sodium ion adsorption on 2D vd W HTSs and providing new insights into material design for alkali atom adsorption.展开更多
We study molybdenum disulfide （MoS2） structures generated by folding single-layer and bilayer MoS2 flakes. We find that this modified layer stacking leads to a decrease in the interlayer coupling and an enhancement ...We study molybdenum disulfide （MoS2） structures generated by folding single-layer and bilayer MoS2 flakes. We find that this modified layer stacking leads to a decrease in the interlayer coupling and an enhancement of the photoluminescence emission yield. We additionally find that folded single-layer MoS2 structures show a contribution to photoluminescence spectra of both neutral and charged excitons, which is a characteristic feature of single-layer MoS2 that has not been observed in multilayer MoS2. The results presented here open the door to fabrication of multilayered MoS2 samples with high optical absorption while maintaining the advantageous enhanced photoluminescence emission of single-layer MoS2 by controllably twisting the MoS2 layers.展开更多
The formation of moirésuperlattices in twisted van der Waals(vdW)homostructures provides a versatile platform for designing the electronic band structure of two-dimensional(2D)materials.In graphene and transition...The formation of moirésuperlattices in twisted van der Waals(vdW)homostructures provides a versatile platform for designing the electronic band structure of two-dimensional(2D)materials.In graphene and transition metal dichalcogenides(TMDs)moirésystems,twist angle has been shown to be a key parameter for regulating the moirésuperlattice.However,the effect of the modulation of the twist angle on moirépotential and interlayer coupling has not been the subject of experimental investigation.Here,we report the observation of the modulation of moirépotential and intralayer excitons in the WS_(2)/WS_(2)homostructure.By accurately adjusting the torsion angle of the homobilayers,the depth of the moirépotential can be modulated.The confinement effect of the moirépotential on the intralayer excitons was further demonstrated by the changing of temperature and valley polarization.Furthermore,we show that a detection of atomic reconstructions by the low-frequency Raman mapping to map out inhomogeneities in moirélattices on a large scale,which endows the uniformity of interlayer coupling.Our results provide insights for an in-depth understanding of the behaviors of moiréexcitons in the twisted van der Waals homostructure,and promote the study of electrical engineering and topological photonics.展开更多
Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals(vdW)interaction at the interface.However,most of the studies focused on the transiti...Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals(vdW)interaction at the interface.However,most of the studies focused on the transition metal dichalcogenide(TMD)/TMD heterostructure,while the interlayer coupling of the TMD/hexagonal boron nitride(h-BN)heterostructure has not been extensively explored despite its importance.In this study,the temperature-dependent interlayer coupling is demonstrated in a heterostructure of molybdenum disulfide(MoS2)and h-BN.The interface between MoS2 and the insulating substrate exerts a significant spectroscopic impact on MoS2 through substrate-induced local strain,charged impurity,and vdW interactions.Under non-resonant conditions,temperature-dependent peak shifts in Raman and photoluminescence(PL)spectra of MoS2 reveal the evolution of interlayer coupling.Phonon frequencies and PL peak energies at different temperatures demonstrate how substrate-induced strain,impurity,and vdW interactions at the interface influence phonon vibration and excitonic transition of MoS2.Under resonant conditions at low temperature,anomalous Raman modes appear in the MoS2/h-BN heterostructure because of the enhanced electron-phonon coupling and vdW interactions.The anomalous Raman modes are quantitatively investigated by the deconvolution of the resonance Raman spectra and described by interlayer coupling at low temperature,in agreement with complementary indications from the temperature-dependent evolution of non-resonant Raman and PL spectra.展开更多
Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device perf...Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance.Nevertheless,the physical picture of interlayer coupling effect during incorporation of monolayer(1L-)hBN is not explicit yet.In this article,spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS_(2)/MoS_(2)and WS_(2)/hBN/MoS_(2)van der Waals heterostructures.We find that 1L-hBN can only slightly block the interlayer electron transfer from WS_(2)layer to MoS_(2)layer.Moreover,insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening.Consequently,the exciton binding energies in WS_(2)/hBN/MoS_(2)heterostructures blueshift comparing to those in WS_(2)/MoS_(2)heterostructures.In this exciton binding energies tuning process,the reducing dielectric screening effect plays a leading role.In the meantime,the quasi-particle(QP)bandgap remains unchanged before and after 1L-hBN insertion,which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other.Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS_(2)/hBN/MoS_(2)heterostructures.展开更多
Van der Waals(vdW)heterobilayers formed by two-dimensional(2D)transition metal dichalcogenides(TMDCs)created a promising platform for various electronic and optical properties,ab initio band results indicate that the ...Van der Waals(vdW)heterobilayers formed by two-dimensional(2D)transition metal dichalcogenides(TMDCs)created a promising platform for various electronic and optical properties,ab initio band results indicate that the band offset of type-Ⅱband alignment in TMDCs vdW heterobilayer could be tuned by introducing Janus WSSe monolayer,instead of an external electric field.On the basis of symmetry analysis,the allowed interlayer hopping channels of TMDCs vdW heterobilayer were determined,and a four-level k·p model was developed to obtain the interlayer hopping.Results indicate that the interlayer coupling strength could be tuned by interlayer electric polarization featured by various band offsets.Moreover,the difference in the formation mechanism of interlayer valley excitons in different TMDCs vdW heterobilayers with various interlayer hopping strength was also clarified.展开更多
The interlayer coupling in van der Waals(vdW)heterostructures(vdWHs)is at the frontier of the fundamental research,underlying many optical behaviors.The graphene/MoS_(2) vdWHs provide an ideal platform to reveal the g...The interlayer coupling in van der Waals(vdW)heterostructures(vdWHs)is at the frontier of the fundamental research,underlying many optical behaviors.The graphene/MoS_(2) vdWHs provide an ideal platform to reveal the good interfacial coupling between graphene and MoS_(2) constituents.Here,three groups of graphene/MoS_(2) vdWHs were prepared by transferring 1–3 layers of graphene onto monolayer MoS_(2).The interlayer coupling within graphene/MoS_(2) vdWHs were characterized and analyzed by Raman spectroscopy,photoluminescence(PL)spectroscopy and optical contrast(OC)spectroscopy.The upshift of the A_(1g) peak of MoS_(2) and the upshift of the D and 2D peaks of SLG show that the electrons move from MoS_(2) to graphene accompanied by the dielectric shielding effect on graphene.The weakened PL intensities and the slight red shift of A peak prove that the electrons move from MoS_(2) to graphene meanwhile the recombination of hole and electron pairs is blocked in vdWHs.Our results deepen the understanding of the interlayer coupling of graphene/MoS_(2) vdWHs and therefore provide guidelines for the practical design and application of optoelectronic devices based on graphene/MoS_(2) vdWHs.展开更多
Interlayer coupling as a unique feature for two-dimensional(2D)materials may influence their thickness-dependent physical properties,especially the bandgap due to quantum confinement effect.Widely-studied 2D materials...Interlayer coupling as a unique feature for two-dimensional(2D)materials may influence their thickness-dependent physical properties,especially the bandgap due to quantum confinement effect.Widely-studied 2D materials usually possess strong interlayer coupling such as most of transition metal dichalcogenides(TMDs),PtS_(2) and so on.However,2D materials with weak interlayer coupling are rarely referred that mainly focus on ReS_(2),as well as its counterpart ReSe_(2).Here we report a new member of weak interlayer coupling 2D materials,germanium disulfide(GeS_(2)).The interlayer interaction in GeS_(2) is investigated from theory to experiment.By density functional theory calculations,we find that this extraordinarily weak interlayer coupling in GeS_(2) originates from the weak hybridization of interlayer S atoms.Thickness-dependent Raman spectra of GeS_(2) flakes exhibit that the Raman peaks remain unchanged when increasing the thickness;and a small first-order temperature coefficient of-0.00857 cm^(-1)·K^(-1) is obtained from the temperature-dependent Raman spectra.These experimental results further confirm the weak interlayer coupling in GeS_(2).展开更多
Two-dimensional transition metal dichalcogenides（TMDs） have attracted extensive attention due to their many novel properties.The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds,...Two-dimensional transition metal dichalcogenides（TMDs） have attracted extensive attention due to their many novel properties.The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds,while van der Waals interactions combine the layers together.This makes its lattice dynamics layer-number dependent.The evolutions of ultralow frequency（〈 50 cm^（-1）） modes,such as shear and layer-breathing modes have been well-established.Here,we review the layer-number dependent high-frequency（〉 50 cm^（-1）） vibration modes in few-layer TMDs and demonstrate how the interlayer coupling leads to the splitting of high-frequency vibration modes,known as Davydov splitting.Such Davydov splitting can be well described by a van der Waals model,which directly links the splitting with the interlayer coupling.Our review expands the understanding on the effect of interlayer coupling on the high-frequency vibration modes in TMDs and other two-dimensional materials.展开更多
Interlayer excitons(IXs) formed in transition metal dichalcogenides(TMDs)/two-dimensional(2 D) perovskite heterostructures are emerging as new platforms in the research of excitons. Compared with IXs in TMD van der Wa...Interlayer excitons(IXs) formed in transition metal dichalcogenides(TMDs)/two-dimensional(2 D) perovskite heterostructures are emerging as new platforms in the research of excitons. Compared with IXs in TMD van der Waals heterostructures, IXs can be robustly formed in TMDs/2 D perovskite heterostructures regardless of the twist angle and thermal annealing process. Efficient control of interlayer coupling is essential for realizing their functionalities and enhancing their performances. Nevertheless, the study on the control of interlayer coupling strength between TMD and 2 D perovskites is elusive. Therefore, we realize the control of interlayer coupling between monolayer WSe_(2) and(iso-BA)_(2)PbI_(4) with SiO_(2) pillars in situ. An abnormal 10-nm blue shift and 2.5 times photoluminescence intensity enhancement were observed for heterostructures on the pillar, which was contrary to the red shift observed in TMD heterobilayers. We attributed the abnormal blue shift to the enhanced interlayer coupling arising from the reduced gap between constituent layers. In addition, IXs became more dominant over intralayer excitons with enhanced coupling. The interlayer coupling could be further engineered by tuning the height(h) and diameter(d)of pillars. In particular, an additional triplet IX showed up for the pillar with an h/d ratio of 0.6 due to the symmetry breaking of monolayer WSe_(2). The symmetry breaking also induced an anisotropic response of IXs. Our study is beneficial for tuning and enhancing the performance of IX-based devices, exciton localization and quantum emitters.展开更多
Nonreciprocal interlayer coupling is difcult to practically implement in bilayer non-Hermitian topological photonic systems.In this work,we identify a similarity transformation between the Hamiltonians of systems with...Nonreciprocal interlayer coupling is difcult to practically implement in bilayer non-Hermitian topological photonic systems.In this work,we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss.The similarity transformation is widely applicable,and we show its application in one-and two-dimensional bilayer topological systems as examples.The bilayer non-Hermitian system with nonreciprocal interlayer coupling,whose topological number can be defned using the gauge-smoothed Wilson loop,is topologically equivalent to the bilayer system with on-site gain/loss.We also show that the topological number of bilayer non-Hermitian C6v-typed domaininduced topological interface states can be defned in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model.Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems.This scheme is useful for observation of non-Hermitian skin efect in three-dimensional systems.展开更多
基金National Natural Science F oundation of China (5 99710 0 1)
文摘Cu/Co, Cu/NiFe, Ta/NiFe bilayers and Co/Cu/Co, Co/Cu/NiFe, Co/Ta/NiFe sandwich films were deposited by a magnetron sputtering method. Magnetic properties were evaluated by VSM and spin valve magnetoresistance was investigated by a four-probe method to study the interlayer coupling of the two magnetic layers. It has been found that the interlayer coupling depended not only on the layer thickness of the nonmagnetic spacer but also on the nature of the spacer. The interlayer coupling was reduced as the spacer layer thickness increased. The result was consistent with those from observations of the magnetic domain for the trilayers by means of Lorentz Electron Microscope. The trilayers with Cu spacer layer have shown a stronger coupling than those with Ta spacer layer.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51772087,11804089,11574350,11904094,and 51972106)the Natural Science Foundation of Hunan Province,China(Grant Nos.2018JJ3025,2019JJ50034,and 2019JJ50073)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB30000000)the Fundamental Research Funds for the Central Universities of China.
文摘Interlayer coupling in layered semiconductors can significantly affect their optoelectronic properties.However,understanding the mechanisms behind the interlayer coupling at the atomic level is not straightforward.Here,we study modulations of the electronic structure induced by the interlayer coupling in theγ-phase of indium selenide(γ-InSe)using scanning probe techniques.We observe a strong dependence of the energy gap on the sample thickness and a small effective mass along the stacking direction,which are attributed to strong interlayer coupling.In addition,the moirépatterns observed inγ-InSe display a small band-gap variation and nearly constant local differential conductivity along the patterns.This suggests that modulation of the electronic structure induced by the moirépotential is smeared out,indicating the presence of a significant interlayer coupling.Our theoretical calculations confirm that the interlayer coupling inγ-InSe is not only of the van der Waals origin,but also exhibits some degree of hybridization between the layers.Strong interlayer coupling might play an important role in the performance ofγ-InSe-based devices.
文摘Fe-Si/Cr multilayers with amorphous Fe-Si magnetic layers and Cr nonmagnetic layers were prepared by an rf-sputtering method.When the thickness of the Cr layers varies from 0.5 to 6 nm, the interlayer coupling oscillates periodically from ferromagnetic to antiferromagnetism. For each sample only one wide uniform resonance peak is detected by the ferromagnetic resonance. The uniform resonance field Hb and the resonance line width △H_b oscillate periodically as the thickness of the Cr layers increases, which is related to the oscillation of the interlayer coupling from ferromagnetic to antiferromagnetism.The oscillation period is about 1.5nm.
基金supported by the Natural Science Foundation of Liaoning Province under Grant No.20041021the Scientific Foundation of the Educational Department of Liaoning Province under Grant Nos.2004C006 and 20060638the Postdoctoral Foundation of Shenyang University of Technology
文摘Spin-wave theory is used to study magnetic properties of ferromagnetic double layers with a ferrimagnetic interlayer coupling at zero temperature. The spin-wave spectra and four sublattices magnetizations and internal energy are calculated by employing retarded Green function technique. The sublattice magnetizations at ground state are smaller than their classical values, owing to the zero-point quantum fluctuations of the spins.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51871127 and 11674187)。
文摘The antiferromagnetic(AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic(FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance(FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, Fe Co B/Ru/Fe Co B sandwich trilayers with Ru thickness(tRu) ranging from 1 A to 16 A are prepared by a compositional gradient sputtering(CGS) method. It is revealed that a stress-induced anisotropy is present in the Fe Co B films due to the B composition gradient in the samples. A tRu-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of 2 A ≤ tRu≤ 8 A and over 16 A, while an FM coupling is present in a range of tRu< 2 A and 9 A ≤ tRu≤ 14.5 A. It is interesting that an ultrahigh optical mode(OM) FMR frequency in excess of 20 GHz is obtained in the sample with tRu= 2.5 A under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of tRuare verified by Layadi’s rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.
基金supported by the Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences,Basic and Applied Basic Research Program of Guangdong Province(No.2021B0301030003)Ji Hua Laboratory(No.X210141TL210)。
文摘The stacking structure of Nb_(2)CSe_(2),a newly synthesized layered metal carbo-selenide,was elucidated by scanning transmission electron microscopy.Nb,CSe2 features Se-Nb-C-Nb-Se quintuple atomic layers.These layers are stacked in Bernal mode.In this mode,Nb,CSe2 crystallizes in a trigonal symmetry(space group P3m1,No.164),with lattice parameters of a=3.33 A and c=18.20 A.Electronic structure calculations indicate that the metal carbo-selenide has Fermi energy crossing the bands where it touches to give a zero gap,indicating that it is an electronic conductor.As evidenced experimentally,the electrical conductivity is as high as 6.6×10^(5) S·m^(-1),outperforming the counterparts in the MXene family.Owing to the layered structure,the bonding in Nb_(2)CSe_(2) with an ionic formula of(Nb^(1.48+)),(C^(1.74-))(Se^(0.61-))_(2) is highly anisotropic,with metallic-covalent-ionic bonding in intralayers and weak bonding between interlayers.The layered nature is further evidenced by elastic properties,interlayer energy,and friction coefficient determination.These characteristics indicate that Nb_(2)CSe_(2) is an analog of molybdenum disulfide(MoS_(2)),which is a typical binary van der Waals(vdW)solid.Moreover,vibrational properties are reported,which may offer an optical identification standardfor new ternary vdW solids in spectroscopic studies,including Raman scatteringand infrared absorption.
基金Project supported by the“Pioneer”and“Leading Goose”R&D Program of Zhejiang Province(Grant No.2022C01053)the Key Research and Development Program of Zhejiang Province(Grant No.2021C01039)+1 种基金the National Natural Science Foundation of China(Grant No.62293493)the Natural Science Foundation of Zhejiang Province,China(Grant No.LQ21A050001)。
文摘Interlayer exchange coupling(IEC)plays a critical role in spin-orbit torque(SOT)switching in synthetic magnets.This work establishes a fundamental correlation between IEC and SOT dynamics within Co/Pt-based synthetic antiferromagnets and synthetic ferromagnets.The antiferromagnetic and ferromagnetic coupling states are precisely engineered through Ruderman-Kittel-Kasuya-Yosida(RKKY)interactions by modulating the Ir spacer thickness.Experimental results reveal that the critical switching current density exhibits a strong positive correlation with the IEC strength,regardless of the coupling type.A comprehensive theoretical framework based on the Landau-Lifshitz-Gilbert equation elucidates how IEC contributes to the effective energy barrier that must be overcome during SOT-induced magnetization switching.Significantly,the antiferromagnetically coupled samples demonstrate enhanced SOT efficiency,with the spin Hall angle being directly proportional to the antiferromagnetic exchange coupling field.These insights establish a coherent physical paradigm for understanding IEC-dependent SOT dynamics and provide strategic design principles for the development of energy-efficient next-generation spintronic devices.
基金supported by the National Key Basic Research Program of China(Grant Nos.2021YFA1400300 and 2023YFA1610400)the National Natural Science Foundation of China(Grant Nos.12204268,52371169,52130103,and U22A20263)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023B1515120015)the Open Research Fund of Songshan Lake Materials Laboratory(Grant No.2022SLABFN13)。
文摘The complex interplay of magnetic interactions at the yttrium iron garnet(YIG)/ferromagnet interface is important for spintronic and magnonic devices.In this study,we present a comprehensive investigation of the interlayer coupling and switching mechanisms in YIG/Py(permalloy)heterostructures based on gadolinium gallium garnet(GGG)and SiO_(2)substrates.We observe antiferromagnetic interlayer coupling between Py and YIG on SiO_(2)substrates,whereas ferromagnetic interlayer coupling is observed on GGG substrates.Using polarized neutron reflectometry with depth-and elementresolved measurements,we obtain an in-depth understanding of the magnetic interactions between the YIG and Py layers.We demonstrate that polycrystalline YIG gives rise to antiferromagnetic interlayer coupling.This work provides valuable insights into designing and controlling magnetic coupling in hybrid structures for spintronic applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.T2325007,62250073,U21A20459,62004026,61774029,62104029,12104086,62150052,U23A20570,and 51902346)the Sichuan Science and Technology Program(Grant Nos.2021JDTD0028,2023NSFSC1334,24NSFSC5852,and 24NSFSC5853)the Science and Technology Innovation Program of Hunan Province(Grant No.2021RC3021)。
文摘Tungsten disulfide(WS_(2))has been reported to show negligible stacking dependence under ambient conditions,impeding its further explorations on physical properties and potential applications.Here,we realize efficient modulation of interlayer coupling in bilayer WS_(2)with 3R and 2H stackings by high pressure,and find that the pressure-triggered interlayer coupling and pressure-induced resonant-to-nonresonant transition exhibit prominent stacking dependence,which are experimentally observed for the first time in WS2.Our work may unleash the stacking degree of freedom in designing WS_(2)devices with tailored properties correlated to interlayer coupling.
基金the financial support by the National Key Research and Development Program of China(No.2019YFA0708700)the National Natural Science Foundation of China(Nos.62305196,U23B2087 and 62375158)+4 种基金the China Postdoctoral Science Foundation(No.GZC20231498)the Qingdao Postdoctoral Innovation Project(No.QDBSH20240102078)the Postdoctoral Innovation Program of Shandong Province(No.SDCX-ZG-202400318)Science and Technology Research Project of Hubei Provincial Department of Education(No.D20212603)Hubei University of Arts and Science(No.2020kypytd002)。
文摘Surface adsorption plays a crucial role in various natural and industrial processes,particularly in the field of energy storage.The adsorption of sodium atoms on 2D layered materials can significantly impact their performance as carriers and electrodes in ion batteries.While it is commonly acknowledged that pristine graphene is not favorable for sodium ion adsorption,the suitability of other 2D materials with similar honeycomb symmetry remains unclear.In this study,we employ systematic first-principles calculations to explore interlayer interactions and electron transfer effects on sodium adsorption on 2D van der Waals(vdW)heterostructures(HTSs)surfaces.Our results demonstrate that sodium adsorption is energetically favorable on these substrates.Moreover,we find that the adsorption strength can be effectively tuned by manipulation of the electron accumulation or depletion of the layer directly interacting with the sodium atom.By stacking these layered materials with different electron abundancy to form vd W HTSs,the charge density of the substrate becomes tunable through interlayer charge transfer.In these vdW HTSs,the adsorption behavior of sodium is primarily controlled by the absorption layer and exhibits a linear correlation with its pz-band center.Additionally,we identify linear correlations between the sodium adsorption energies,the electron loss of the sodium atom,the interlayer charge transfer,and the heights of the adsorbed sodium atom.These discoveries underscore the impact of interlayer electron transfer and interactions on sodium ion adsorption on 2D vd W HTSs and providing new insights into material design for alkali atom adsorption.
文摘We study molybdenum disulfide （MoS2） structures generated by folding single-layer and bilayer MoS2 flakes. We find that this modified layer stacking leads to a decrease in the interlayer coupling and an enhancement of the photoluminescence emission yield. We additionally find that folded single-layer MoS2 structures show a contribution to photoluminescence spectra of both neutral and charged excitons, which is a characteristic feature of single-layer MoS2 that has not been observed in multilayer MoS2. The results presented here open the door to fabrication of multilayered MoS2 samples with high optical absorption while maintaining the advantageous enhanced photoluminescence emission of single-layer MoS2 by controllably twisting the MoS2 layers.
基金the National Natural Science Foundation of China(No.61775241)Hunan Provincial Science Fund for Distinguished Young Scholars(No.2020JJ2059)+3 种基金the Youth Innovation Team(No.2019012)of CSU,Hunan province key research and development project(No.2019GK2233)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20190806144418859)support of the High-Performance Complex Manufacturing Key State Lab Project,Central South University(No.ZZYJKT2020-12)Z.W.L.thanks the support from the Australian Research Council(ARC Discovery Project,DP180102976).
文摘The formation of moirésuperlattices in twisted van der Waals(vdW)homostructures provides a versatile platform for designing the electronic band structure of two-dimensional(2D)materials.In graphene and transition metal dichalcogenides(TMDs)moirésystems,twist angle has been shown to be a key parameter for regulating the moirésuperlattice.However,the effect of the modulation of the twist angle on moirépotential and interlayer coupling has not been the subject of experimental investigation.Here,we report the observation of the modulation of moirépotential and intralayer excitons in the WS_(2)/WS_(2)homostructure.By accurately adjusting the torsion angle of the homobilayers,the depth of the moirépotential can be modulated.The confinement effect of the moirépotential on the intralayer excitons was further demonstrated by the changing of temperature and valley polarization.Furthermore,we show that a detection of atomic reconstructions by the low-frequency Raman mapping to map out inhomogeneities in moirélattices on a large scale,which endows the uniformity of interlayer coupling.Our results provide insights for an in-depth understanding of the behaviors of moiréexcitons in the twisted van der Waals homostructure,and promote the study of electrical engineering and topological photonics.
基金This work was supported by the Creative Materials Discovery Program(No.2016M3D1A1900035)the Basic Research Program(No.2019R1A2C2009171)through the National Research Foundation(NRF)funded by the Ministry of Science and ICT,Republic of Korea.
文摘Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals(vdW)interaction at the interface.However,most of the studies focused on the transition metal dichalcogenide(TMD)/TMD heterostructure,while the interlayer coupling of the TMD/hexagonal boron nitride(h-BN)heterostructure has not been extensively explored despite its importance.In this study,the temperature-dependent interlayer coupling is demonstrated in a heterostructure of molybdenum disulfide(MoS2)and h-BN.The interface between MoS2 and the insulating substrate exerts a significant spectroscopic impact on MoS2 through substrate-induced local strain,charged impurity,and vdW interactions.Under non-resonant conditions,temperature-dependent peak shifts in Raman and photoluminescence(PL)spectra of MoS2 reveal the evolution of interlayer coupling.Phonon frequencies and PL peak energies at different temperatures demonstrate how substrate-induced strain,impurity,and vdW interactions at the interface influence phonon vibration and excitonic transition of MoS2.Under resonant conditions at low temperature,anomalous Raman modes appear in the MoS2/h-BN heterostructure because of the enhanced electron-phonon coupling and vdW interactions.The anomalous Raman modes are quantitatively investigated by the deconvolution of the resonance Raman spectra and described by interlayer coupling at low temperature,in agreement with complementary indications from the temperature-dependent evolution of non-resonant Raman and PL spectra.
基金the National Natural Science Foundation of China(Nos.11674062,61775042,and 61774040)the Fudan University-CIOMP Joint Fund(Nos.FC2019-004,FC2019-006,and FC2018-002)+2 种基金the National Key R&D Program of China(No.2018YFA0703700)the Shanghai Municipal Science and Technology Commission(No.18JC1410300)the Shanghai Municipal Natural Science Foundation(No.20ZR1403200).
文摘Inserting hexagonal boron nitride(hBN)as barrier layers into bilayer transition metal dichalcogenides heterointerface has been proved an efficient method to improve two dimensional tunneling optoelectronic device performance.Nevertheless,the physical picture of interlayer coupling effect during incorporation of monolayer(1L-)hBN is not explicit yet.In this article,spectroscopic ellipsometry was used to experimentally obtain the broadband excitonic and critical point properties of WS_(2)/MoS_(2)and WS_(2)/hBN/MoS_(2)van der Waals heterostructures.We find that 1L-hBN can only slightly block the interlayer electron transfer from WS_(2)layer to MoS_(2)layer.Moreover,insertion of 1L-hBN weakens the interlayer coupling effect by releasing quantum confinement and reducing efficient dielectric screening.Consequently,the exciton binding energies in WS_(2)/hBN/MoS_(2)heterostructures blueshift comparing to those in WS_(2)/MoS_(2)heterostructures.In this exciton binding energies tuning process,the reducing dielectric screening effect plays a leading role.In the meantime,the quasi-particle(QP)bandgap remains unchanged before and after 1L-hBN insertion,which is attributed to released quantum confinement and decreased dielectric screening effects canceling each other.Unchanged QP bandgap as along with blueshift exciton binding energies lead to the redshift exciton transition energies in WS_(2)/hBN/MoS_(2)heterostructures.
基金supported by the National Natural Science Foundation of China(No.51872170)Young Scholars Program of Shandong University(YSPSDU)+2 种基金Shandong Provincial Key Research and Development Program(Major Scientific and Technological Innovation Project)(No.2019JZZY010302)the Natural Science Foundation of Shandong Province(No.ZR2019MEM013)Taishan Scholar Program of Shandong Province.
文摘Van der Waals(vdW)heterobilayers formed by two-dimensional(2D)transition metal dichalcogenides(TMDCs)created a promising platform for various electronic and optical properties,ab initio band results indicate that the band offset of type-Ⅱband alignment in TMDCs vdW heterobilayer could be tuned by introducing Janus WSSe monolayer,instead of an external electric field.On the basis of symmetry analysis,the allowed interlayer hopping channels of TMDCs vdW heterobilayer were determined,and a four-level k·p model was developed to obtain the interlayer hopping.Results indicate that the interlayer coupling strength could be tuned by interlayer electric polarization featured by various band offsets.Moreover,the difference in the formation mechanism of interlayer valley excitons in different TMDCs vdW heterobilayers with various interlayer hopping strength was also clarified.
基金This work is supported by the National Natural Science foundation of China(NSFC)(No.11904154)Hebei Province Natural Science Foundation(A2020201028).
文摘The interlayer coupling in van der Waals(vdW)heterostructures(vdWHs)is at the frontier of the fundamental research,underlying many optical behaviors.The graphene/MoS_(2) vdWHs provide an ideal platform to reveal the good interfacial coupling between graphene and MoS_(2) constituents.Here,three groups of graphene/MoS_(2) vdWHs were prepared by transferring 1–3 layers of graphene onto monolayer MoS_(2).The interlayer coupling within graphene/MoS_(2) vdWHs were characterized and analyzed by Raman spectroscopy,photoluminescence(PL)spectroscopy and optical contrast(OC)spectroscopy.The upshift of the A_(1g) peak of MoS_(2) and the upshift of the D and 2D peaks of SLG show that the electrons move from MoS_(2) to graphene accompanied by the dielectric shielding effect on graphene.The weakened PL intensities and the slight red shift of A peak prove that the electrons move from MoS_(2) to graphene meanwhile the recombination of hole and electron pairs is blocked in vdWHs.Our results deepen the understanding of the interlayer coupling of graphene/MoS_(2) vdWHs and therefore provide guidelines for the practical design and application of optoelectronic devices based on graphene/MoS_(2) vdWHs.
基金supported by the National Natural Science Foundation of China(Nos.21922512,21972147,21875264,61725401,and 11964032)the Youth Innovation Promotion Association CAS(No.2017050)the National Natural Science Foundation of Guizhou Province(Nos.KY[2019]060,[2020]123,and trxyDH1905).
文摘Interlayer coupling as a unique feature for two-dimensional(2D)materials may influence their thickness-dependent physical properties,especially the bandgap due to quantum confinement effect.Widely-studied 2D materials usually possess strong interlayer coupling such as most of transition metal dichalcogenides(TMDs),PtS_(2) and so on.However,2D materials with weak interlayer coupling are rarely referred that mainly focus on ReS_(2),as well as its counterpart ReSe_(2).Here we report a new member of weak interlayer coupling 2D materials,germanium disulfide(GeS_(2)).The interlayer interaction in GeS_(2) is investigated from theory to experiment.By density functional theory calculations,we find that this extraordinarily weak interlayer coupling in GeS_(2) originates from the weak hybridization of interlayer S atoms.Thickness-dependent Raman spectra of GeS_(2) flakes exhibit that the Raman peaks remain unchanged when increasing the thickness;and a small first-order temperature coefficient of-0.00857 cm^(-1)·K^(-1) is obtained from the temperature-dependent Raman spectra.These experimental results further confirm the weak interlayer coupling in GeS_(2).
基金Project supported by the National Basic Research Program of China(No.2016YFA0301200)the National Natural Science Foundation of China(Nos.11225421,11474277,11434010,61474067,11604326,11574305 and 51527901)the National Young 1000 Talent Plan of China
文摘Two-dimensional transition metal dichalcogenides（TMDs） have attracted extensive attention due to their many novel properties.The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds,while van der Waals interactions combine the layers together.This makes its lattice dynamics layer-number dependent.The evolutions of ultralow frequency（〈 50 cm^（-1）） modes,such as shear and layer-breathing modes have been well-established.Here,we review the layer-number dependent high-frequency（〉 50 cm^（-1）） vibration modes in few-layer TMDs and demonstrate how the interlayer coupling leads to the splitting of high-frequency vibration modes,known as Davydov splitting.Such Davydov splitting can be well described by a van der Waals model,which directly links the splitting with the interlayer coupling.Our review expands the understanding on the effect of interlayer coupling on the high-frequency vibration modes in TMDs and other two-dimensional materials.
基金supported by the National Key Research and Development Program of China (2018YFA0704403)the National Natural Science Foundation of China (62005091 and 62074064)+1 种基金Hubei Provincial Natural Science Foundation (2020CFB194)Huazhong University of Science and Technology (HUST) grant (2019kfy XJJS046)。
文摘Interlayer excitons(IXs) formed in transition metal dichalcogenides(TMDs)/two-dimensional(2 D) perovskite heterostructures are emerging as new platforms in the research of excitons. Compared with IXs in TMD van der Waals heterostructures, IXs can be robustly formed in TMDs/2 D perovskite heterostructures regardless of the twist angle and thermal annealing process. Efficient control of interlayer coupling is essential for realizing their functionalities and enhancing their performances. Nevertheless, the study on the control of interlayer coupling strength between TMD and 2 D perovskites is elusive. Therefore, we realize the control of interlayer coupling between monolayer WSe_(2) and(iso-BA)_(2)PbI_(4) with SiO_(2) pillars in situ. An abnormal 10-nm blue shift and 2.5 times photoluminescence intensity enhancement were observed for heterostructures on the pillar, which was contrary to the red shift observed in TMD heterobilayers. We attributed the abnormal blue shift to the enhanced interlayer coupling arising from the reduced gap between constituent layers. In addition, IXs became more dominant over intralayer excitons with enhanced coupling. The interlayer coupling could be further engineered by tuning the height(h) and diameter(d)of pillars. In particular, an additional triplet IX showed up for the pillar with an h/d ratio of 0.6 due to the symmetry breaking of monolayer WSe_(2). The symmetry breaking also induced an anisotropic response of IXs. Our study is beneficial for tuning and enhancing the performance of IX-based devices, exciton localization and quantum emitters.
基金supported by the National Natural Science Foundation of China(Nos.91950204,92150302,and 62175009)Innovation Program for Quantum Science and Technology(No.2021ZD0301500)Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics(No.KF202114).
文摘Nonreciprocal interlayer coupling is difcult to practically implement in bilayer non-Hermitian topological photonic systems.In this work,we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss.The similarity transformation is widely applicable,and we show its application in one-and two-dimensional bilayer topological systems as examples.The bilayer non-Hermitian system with nonreciprocal interlayer coupling,whose topological number can be defned using the gauge-smoothed Wilson loop,is topologically equivalent to the bilayer system with on-site gain/loss.We also show that the topological number of bilayer non-Hermitian C6v-typed domaininduced topological interface states can be defned in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model.Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems.This scheme is useful for observation of non-Hermitian skin efect in three-dimensional systems.
