Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilay...Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilayer transition metal dichalcogenides(TMDs)lead to zone folding and miniband formation in the resulting electronic bands,holding the promise to exhibit inter-layer excitonic optical phenomena.Although some experiments have shown the existence of twist-angle-dependent intra-and inter-layer excitons in twisted MoSe2 homobilayers,electrical control of the interlayer excitons in MoSe_(2) is relatively under-explored.Here,we show the signatures of the moiréeffect on intralayer and interlayer excitons in 2H-stacked twisted MoSe2 homobilayers.Doping-and electric field-dependent photoluminescence mea-surements at low temperatures give evidence of the momentum-direct K-K intralayer excitons,and the momentum-indirect Г-K and Г-Q interlayer excitons.Our results suggest that twisted MoSe_(2) homobilayers are an intriguing platform for engineering interlayer exciton states,which may shed light on future atomically thin optoelectronic applications.展开更多
The assembly of monolayer transition metal dichalcogenides(TMDs)in van der Waals heterostructures yields the formation of spatially separated interlayer excitons(IXs)with large binding energies,long lifetimes,permanen...The assembly of monolayer transition metal dichalcogenides(TMDs)in van der Waals heterostructures yields the formation of spatially separated interlayer excitons(IXs)with large binding energies,long lifetimes,permanent dipole moments and valley-contrasting physics,providing a compelling platform for investigating and engineering spatiotemporal IX propagation with highly tunable dynamics.Further twisting the stacked TMD monolayers can create long-term periodic moirépatterns with spatially modified band structures and varying moirépotentials,featuring tailored traps that can induce strong correlations with density–dependent phase transitions to modulate the exciton transport.The rich exciton landscapes in TMD heterostructures,combined with advancements in valleytronics and twistronics,hold great promise for exploring exciton-integrated circuits base on manipulation of exciton diffusion and transport.In this Review,we provide a comprehensive overview of recent progress in understanding IXs and moiréexcitons,with a specific focus on emerging exciton diffusion and transport in TMD heterostructures.We put emphasis on spatial manipulation of exciton flux through various methods,encompassing exciton density,dielectric environment,electric field and structure engineering,for precise control.This ability to manipulate exciton diffusion opens up new possibilities for interconverting optical communication and signal processing,paving the way for exciting applications in high-performance optoelectronics,such as excitonic devices,valleytronic transistors and photodetectors.We finally conclude this review by outlining perspectives and challenges in harnessing IX currents for next-generation optoelectronic applications.展开更多
In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticl...In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticle excitations including holons,doublons and interlayer exciton insulators.Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators.Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier.The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites.For the interlayer exciton insulator consisting of a holon and a carrier in different layers,we have also obtained its effective Bohr radius and energy splitting between the ground and the first-excited states.展开更多
Vertically stacked transition metal dichalcogenide(TMD)heterostructures provide an opportunity to explore optoelectronic properties within the two-dimensional limit.In such structures,spatially indirect interlayer exc...Vertically stacked transition metal dichalcogenide(TMD)heterostructures provide an opportunity to explore optoelectronic properties within the two-dimensional limit.In such structures,spatially indirect interlayer excitons(IXs)can be generated in adjacent layers because of strong Coulomb interactions.However,due to the complexity of the multilayered heterostructure(HS),the capture and study of the IXs in trilayer type-Ⅱ HSs have so far remained elusive.Here,we present the observation of the IXs in trilayer type-Ⅱ staggered band alignment of MoS_(2)/MoSe_(2)/WSe_(2) van der Waals(vdW)HSs by photoluminescence(PL)spectroscopy.The central energy of IX is 1.33 eV,and the energy difference between the extracted double peaks is 23 meV.We confirmed the origin of IX through PL properties and calculations by the density functional theory,we also studied the dependence of the IX emission peak on laser power and temperature.Furthermore,the polarization-resolved PL spectra of HS were also investigated,and the maximum polarizability of the emission peak of WSe_(2) reached 11.40%at 6 K.Our findings offer opportunities for the study of new physical properties of excitons in TMD HSs and therefore are valuable for exploring the potential applications of TMDs in optoelectronic devices.展开更多
Moirématerials,composed of two single-layer two-dimensional semiconductors,are important because they are good platforms for studying strongly correlated physics.Among them,moirématerials based on transition...Moirématerials,composed of two single-layer two-dimensional semiconductors,are important because they are good platforms for studying strongly correlated physics.Among them,moirématerials based on transition metal dichalcogenides(TMDs)have been intensively studied.The hetero-bilayer can support moiréinterlayer excitons if there is a small twist angle or small lattice constant difference between the TMDs in the hetero-bilayer and form a type-Ⅱ band alignment.The coupling of moiréinterlayer excitons to cavity modes can induce exotic phenomena.Here,we review recent advances in the coupling of moiréinterlayer excitons to cavities,and comment on the current difficulties and possible future research directions in this field.展开更多
Highly efficient and stable hybrid white organic light-emitting diodes （HWOLEDs） with a mixed bipolar interlayer between fluorescent blue and phosphorescent yellow emitting layers are demonstrated. The bipolar inter...Highly efficient and stable hybrid white organic light-emitting diodes （HWOLEDs） with a mixed bipolar interlayer between fluorescent blue and phosphorescent yellow emitting layers are demonstrated. The bipolar interlayer is a mixture of p-type diphenyl （l0-phenyl-lOH-spiro [acridine-9,9＇-fluoren]-3Lyl） phosphine oxide and n-type 2＇,2- （1,3,5-benzinetriyl）-tris（1-phenyl-l-H-benzimidazole）. The electroluminance and Commission Internationale de l＇Eclairage （CIE1931） coordinates＇ characteristics can be modulated easily by adjusting the ratio of the hole- predominated material to the electron-predominated material in the interlayer. The hybrid WOLED with a p-type：n-type ratio of 1：3 shows a maximum current efficiency and power efficiency of 61.1 ed/A and 55.8 lm/W, respectively, with warm white CIE coordinates of （0.34, 0.43）. The excellent efficiency and adaptive CIE coordi- nates are attributed to the mixed interlayer with improved charge carrier balance, optimized exciton distribution, and enhanced harvesting of singlet and triplet excitons.展开更多
Two-dimensional(2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo-or ...Two-dimensional(2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo-or heterojunctions, which show novel emission properties caused by interface engineering. In this review, we will first give an overview of the basic strategies that have been employed in interface engineering, including changing components, adjusting interlayer gap, and tuning twist angle. By modifying the interfacial factors, novel emission properties of emerging excitons are unveiled and discussed. Generally, well-tailored interfacial energy transfer and charge transfer within a 2D heterostructure cause static modulation of the brightness of intralayer excitons. As a special case, dynamically correlated dual-color emission in weakly-coupled bilayers will be introduced, which originates from intermittent interlayer charge transfer. For homobilayers and type Ⅱ heterobilayers, interlayer excitons with electrons and holes residing in neighboring layers are another important topic in this review. Moreover, the overlap of two crystal lattices forms moiré patterns with a relatively large period, taking effect on intralayer and interlayer excitons. Particularly, theoretical and experimental progresses on spatially modulated moiré excitons with ultra-sharp linewidth and quantum emission properties will be highlighted. Moiré quantum emitter provides uniform and integratable arrays of single photon emitters that are previously inaccessible, which is essential in quantum many-body simulation and quantum information processing. Benefiting from the optically addressable spin and valley indices, 2D heterostructures have become an indispensable platform for investigating exciton physics, designing and integrating novel concept emitters.展开更多
Van der Waals heterostructures have recently emerged,in which two distinct transitional metal dichalcogenide(TMD)monolayers are stacked vertically to generate interlayer excitons(IXs),offing new opportunites for the d...Van der Waals heterostructures have recently emerged,in which two distinct transitional metal dichalcogenide(TMD)monolayers are stacked vertically to generate interlayer excitons(IXs),offing new opportunites for the design of optoelectronic devices.However,the bilayer heterostructure with type-II band alignment can only produce low quantum yield.Here,we present the observation of interlayer neutral excitons and trions in the MoSe_(2)/MoS_(2)/MoSe_(2)trilayer heterostructure(Tri-HS).In comparison to the 8 K bilayer heterostructure,the addition of a MoSe_(2)layer to the Tri-HS can significantly increase the quantum yield of IXs.It is believed the two symmetrical type-II band alignments formed in the Tri-HS could effectively promote the IX radiation recombination.By analyzing the photoluminescence(PL)spectrum of the IXs at cryogenic temperature and the power dependence,the existence of the interlayer trions was confirmed.Our results provide a promising platform for the development of more efficient optoelectronic devices and the investigation of new physical properties of TMDs.展开更多
Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic pr...Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.展开更多
Due to the large exciton binding energy,two-dimensional(2D)transition metal dichalcogenides(TMDCs)provide an ideal platform for studying excitonic states and related photonics and optoelectronics.Polarization states l...Due to the large exciton binding energy,two-dimensional(2D)transition metal dichalcogenides(TMDCs)provide an ideal platform for studying excitonic states and related photonics and optoelectronics.Polarization states lead to distinct light-matter interactions which are of great importance for device applications.In this work,we study polarized photoluminescence spectra from intralayer exciton and indirect exciton in WS_(2) and WSe_(2) atomic layers,and interlayer exciton in WS_(2)/WSe_(2) heterostructures by radially and azimuthally polarized cylindrical vector laser beams.We demonstrated the same in-plane and out-of-plane polarization behavior from the intralayer and indirect exciton.Moreover,with these two laser modes,we obtained interlayer exciton in WS_(2)/WSe_(2) heterostructures with stronger out-of-plane polarization,due to the formation of vertical electric dipole moment.展开更多
Stacking single layers of atoms on top of each other provides a fundamental way to achieve novel material systems and engineer their physical properties,which offers opportunities for exploring fundamental physics and...Stacking single layers of atoms on top of each other provides a fundamental way to achieve novel material systems and engineer their physical properties,which offers opportunities for exploring fundamental physics and realizing next-generation optoelectronic devices.Among the two-dimensional(2D)-stacked systems,transition metal dichalcogenide(TMDC)heterostructures are particularly attractive because they host tightly-bonded interlayer excitons which possess various novel and appealing properties.These interlayer excitons have drawn significant research attention and hold high potential for the application in unique optoelectronic devices,such as polarization-and wavelength-tunable single photon emitters,valley Hall transistors,and possible high-temperature superconductors.The development of these devices requires a comprehensive understanding of the fundamental properties of these interlayer excitons and the impact of electric fields on their behaviors.In this review,we summarize the recent advances on the understanding of interlayer exciton dynamics under electric fields in TMDC heterostructures.We put emphasis on the electrical modulation of interlayer excitons’emission,the valley Hall transport of charge carriers after the separation of interlayer excitons by an electric field,and the correlation physics of interlayer excitons and charges under electrical doping and tuning.Challenges and perspectives are finally discussed for the application of TMDC heterostructures in future optoelectronics.展开更多
Interlayer excitons(IXS)are electron–hole pairs bound in the spatial separation layer by the Coulomb effect,and their lifetime is several orders of magnitude longer than that of direct excitons,providing an essential...Interlayer excitons(IXS)are electron–hole pairs bound in the spatial separation layer by the Coulomb effect,and their lifetime is several orders of magnitude longer than that of direct excitons,providing an essential platform for long-lived exciton devices.The recent emergence of the van der Waals heterostructure(HS),which combines two layers of different transitional metal dichalcogenides(TMDs),has created new opportunities for IX research.Herein,we demonstrate the observation of double indirect interlayer excitons in the MoSe_(2)/WSe_(2)HS using photoluminescence(PL)spectroscopy.The intensities of the two peaks are essentially the same,and the energy difference is 22 meV,which is perfectly in line with the calculation result of density functional theory.Furthermore,the experience of variable excitation power also proves that the splitting of the IXs originates from the conduction band spin-splitting of MoSe_(2).The observation results provide a promising platform for further exploring the new physical properties and optoelectronic phenomena of TMD HS.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
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
Excitonic devices are an emerging class of technology that utilizes excitons as carriers for encoding, transmitting, and storing information. Van der Waals heterostructures based on transition metal dichalcogenides of...Excitonic devices are an emerging class of technology that utilizes excitons as carriers for encoding, transmitting, and storing information. Van der Waals heterostructures based on transition metal dichalcogenides often exhibit a type II band alignment, which facilitates the generation of interlayer excitons. As a bonded pair of electrons and holes in the separation layer, interlayer excitons offer the chance to investigate exciton transport due to their intrinsic out-of-plane dipole moment and extended exciton lifetime. Furthermore, interlayer excitons can potentially analyze other encoding strategies for information processing beyond the conventional utilization of spin and charge. The review provided valuable insights and recommendations for researchers studying interlayer excitonic devices within van der Waals heterostructures based on transition metal dichalcogenides. Firstly, we provide an overview of the essential attributes of transition metal dichalcogenide materials, focusing on their fundamental properties, excitonic effects, and the distinctive features exhibited by interlayer excitons in van der Waals heterostructures. Subsequently, this discourse emphasizes the recent advancements in interlayer excitonic devices founded on van der Waals heterostructures, with specific attention is given to the utilization of valley electronics for information processing, employing the valley index. In conclusion, this paper examines the potential and current challenges associated with excitonic devices.展开更多
The development of information processing devices with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momen...The development of information processing devices with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and two-dimensional (2D) heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-orbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given.展开更多
Two-dimensional transition metal dichalcogenides(TMDCs)have been regarded as an intriguing platform for exploring novel physical phenomena and optoelectronic devices due to their excitonic emission characteristics der...Two-dimensional transition metal dichalcogenides(TMDCs)have been regarded as an intriguing platform for exploring novel physical phenomena and optoelectronic devices due to their excitonic emission characteristics derived from the atomic thin thickness and reduced dielectric screening effect.Notably,monolayer TMDCs with a direct bandgap exhibiting strong photoluminescence(PL)are promising candidates for the light-emitting devices,while the interlayer excitons in heterostructures hold great potential for the photonic chips and optical communication applications.However,the non-ideal photoluminescent intensity and quality due to the ultrathin thickness and high defect density of experimentally obtained monolayer TMDCs limit the further development for the light-emission applications.Here,we summarize the research progress on the PL manipulation of the excitonic emission in TMDCs,where the PL intensity enhancement and emission wavelength regulation are included.The concept and characteristics of excitons are overviewed firstly,followed by the discussion on the evaluation and characterization of excitonic emission.The state-of-the-art progress on the manipulation of the neutral excitons and interlayer excitons PL are then summarized.Finally,the challenges and prospects are proposed.展开更多
Photoinduced interfacial charge transfer plays a critical role in energy conversion involving van der Waals(vdW)heterostructures constructed of inorganic nanostructures and organic materials.However,the effect of mole...Photoinduced interfacial charge transfer plays a critical role in energy conversion involving van der Waals(vdW)heterostructures constructed of inorganic nanostructures and organic materials.However,the effect of molecular stacking configurations on charge transfer dynamics is less understood.In this study,we demonstrated the tunability of interfacial charge separation in a type-Ⅱ heterojunction between monolayer(ML)WS_(2) and an organic semiconducting molecule[2-(3″′,4′-dimethyl-[2,2′:5′,2′:5″,2″′-quaterthiophen]-5-yl)ethan-1-ammonium halide(4Tm)]by rational design of relative stacking configurations.The assembly between ML-WS_(2) and the 4Tm molecule forms a face-to-face stacking when 4Tm molecules are in a selfaggregation state.In contrast,a face-to-edge stacking is observed when 4Tm molecule is incorporated into a 2D organic-inorganic hybrid perovskite lattice.The face-to-face stacking was proved to be more favorable for hole transfer from WS_(2) to 4Tm and led to interlayer excitons(IEs)emission.Transient absorption measurements show that the hole transfer occurs on a time scale of 150 fs.On the other hand,the face-to-edge stacking resulted in much slower hole transfer without formation of IEs.This inefficient hole transfer occurs on a similar time scale as A exciton recombination in WS_(2),leading to the formation of negative trions.These investigations offer important fundamental insights into the charge transfer processes at organic−inorganic interfaces.展开更多
基金supported by the National Key R&D Program of China(No.2023YFF1500600)the National Natural Science Foun-dation of China(Nos.12004259,12204287)+3 种基金China Postdoc-toral Science Foundation(Grant No.2022M723215)Zheng Vitto Han acknowledges the support of the Fund for Shanxi“1331 Project”Key Subjects Construction,and the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302003)Kenji Watanabe and Takashi Taniguchi acknowledge support from the JSPS KAKENHI(Grant Nos.20H00354 and 23H02052)the World Premier International Research Center Initiative(WPI),MEXT,Japan.
文摘Twist,the very degree of freedom in van der Waals heterostructures,offers a compelling avenue to manipulate and tailor their electrical and optical characteristics.In particular,moirépatterns in twisted homobilayer transition metal dichalcogenides(TMDs)lead to zone folding and miniband formation in the resulting electronic bands,holding the promise to exhibit inter-layer excitonic optical phenomena.Although some experiments have shown the existence of twist-angle-dependent intra-and inter-layer excitons in twisted MoSe2 homobilayers,electrical control of the interlayer excitons in MoSe_(2) is relatively under-explored.Here,we show the signatures of the moiréeffect on intralayer and interlayer excitons in 2H-stacked twisted MoSe2 homobilayers.Doping-and electric field-dependent photoluminescence mea-surements at low temperatures give evidence of the momentum-direct K-K intralayer excitons,and the momentum-indirect Г-K and Г-Q interlayer excitons.Our results suggest that twisted MoSe_(2) homobilayers are an intriguing platform for engineering interlayer exciton states,which may shed light on future atomically thin optoelectronic applications.
基金the financial support from National Key Research and Development Program of China(2018YFA0704403)National Natural Science Foundation of China(NSFC)(62074064)+1 种基金Natural Science Foundation of Xiamen City(3502Z202471047)the Innovation Fund of WNLO and Research Foundation of Jimei University(ZQ2024004).
文摘The assembly of monolayer transition metal dichalcogenides(TMDs)in van der Waals heterostructures yields the formation of spatially separated interlayer excitons(IXs)with large binding energies,long lifetimes,permanent dipole moments and valley-contrasting physics,providing a compelling platform for investigating and engineering spatiotemporal IX propagation with highly tunable dynamics.Further twisting the stacked TMD monolayers can create long-term periodic moirépatterns with spatially modified band structures and varying moirépotentials,featuring tailored traps that can induce strong correlations with density–dependent phase transitions to modulate the exciton transport.The rich exciton landscapes in TMD heterostructures,combined with advancements in valleytronics and twistronics,hold great promise for exploring exciton-integrated circuits base on manipulation of exciton diffusion and transport.In this Review,we provide a comprehensive overview of recent progress in understanding IXs and moiréexcitons,with a specific focus on emerging exciton diffusion and transport in TMD heterostructures.We put emphasis on spatial manipulation of exciton flux through various methods,encompassing exciton density,dielectric environment,electric field and structure engineering,for precise control.This ability to manipulate exciton diffusion opens up new possibilities for interconverting optical communication and signal processing,paving the way for exciting applications in high-performance optoelectronics,such as excitonic devices,valleytronic transistors and photodetectors.We finally conclude this review by outlining perspectives and challenges in harnessing IX currents for next-generation optoelectronic applications.
基金support by the National Natural Sci-ence Foundation of China(Grant No.12274477)the De-partment of Science and Technology of Guangdong Provincein China(Grant No.2019QN01X061)。
文摘In moiré-patterned van der Waals structures of transition metal dichalcogenides,correlated insulators can form under integer and fractional fillings,whose transport properties are governed by various quasiparticle excitations including holons,doublons and interlayer exciton insulators.Here we theoretically investigate the nearest-neighbor inter-site hoppings of holons and interlayer exciton insulators.Our analysis indicates that these hopping strengths are significantly enhanced compared to that of a single carrier.The underlying mechanism can be attributed to the strong Coulomb interaction between carriers at different sites.For the interlayer exciton insulator consisting of a holon and a carrier in different layers,we have also obtained its effective Bohr radius and energy splitting between the ground and the first-excited states.
基金the support of the Hunan Province’s Key Research and Development Project(No.2019GK2233)the National Natural Science Foundation of China(No.61775241)+4 种基金the Hunan Science Fund for Distinguished Young Scholar(No.2020JJ2059)Youth Innovation Team(No.2019012)of CSU,Hunan Province Graduate Research and Innovation Project(No.CX20190177)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20190806144418859)the support from the Central South University of the State Key Laboratory of High-Performance Complex Manufacturing Project(No.ZZYJKT2020-12).support from the Australian Research Council(ARC Discovery Projects,Nos.DP210103539,DP180102976,and DP130104231).
文摘Vertically stacked transition metal dichalcogenide(TMD)heterostructures provide an opportunity to explore optoelectronic properties within the two-dimensional limit.In such structures,spatially indirect interlayer excitons(IXs)can be generated in adjacent layers because of strong Coulomb interactions.However,due to the complexity of the multilayered heterostructure(HS),the capture and study of the IXs in trilayer type-Ⅱ HSs have so far remained elusive.Here,we present the observation of the IXs in trilayer type-Ⅱ staggered band alignment of MoS_(2)/MoSe_(2)/WSe_(2) van der Waals(vdW)HSs by photoluminescence(PL)spectroscopy.The central energy of IX is 1.33 eV,and the energy difference between the extracted double peaks is 23 meV.We confirmed the origin of IX through PL properties and calculations by the density functional theory,we also studied the dependence of the IX emission peak on laser power and temperature.Furthermore,the polarization-resolved PL spectra of HS were also investigated,and the maximum polarizability of the emission peak of WSe_(2) reached 11.40%at 6 K.Our findings offer opportunities for the study of new physical properties of excitons in TMD HSs and therefore are valuable for exploring the potential applications of TMDs in optoelectronic devices.
基金supported by the National Key R&D Program of China(Grant No.2018YFA036900)the Beijing Natural Science Foundation(Grant No.JQ21018)。
文摘Moirématerials,composed of two single-layer two-dimensional semiconductors,are important because they are good platforms for studying strongly correlated physics.Among them,moirématerials based on transition metal dichalcogenides(TMDs)have been intensively studied.The hetero-bilayer can support moiréinterlayer excitons if there is a small twist angle or small lattice constant difference between the TMDs in the hetero-bilayer and form a type-Ⅱ band alignment.The coupling of moiréinterlayer excitons to cavity modes can induce exotic phenomena.Here,we review recent advances in the coupling of moiréinterlayer excitons to cavities,and comment on the current difficulties and possible future research directions in this field.
基金Supported by the National Natural Science Foundation of China under Grant No 91441201
文摘Highly efficient and stable hybrid white organic light-emitting diodes （HWOLEDs） with a mixed bipolar interlayer between fluorescent blue and phosphorescent yellow emitting layers are demonstrated. The bipolar interlayer is a mixture of p-type diphenyl （l0-phenyl-lOH-spiro [acridine-9,9＇-fluoren]-3Lyl） phosphine oxide and n-type 2＇,2- （1,3,5-benzinetriyl）-tris（1-phenyl-l-H-benzimidazole）. The electroluminance and Commission Internationale de l＇Eclairage （CIE1931） coordinates＇ characteristics can be modulated easily by adjusting the ratio of the hole- predominated material to the electron-predominated material in the interlayer. The hybrid WOLED with a p-type：n-type ratio of 1：3 shows a maximum current efficiency and power efficiency of 61.1 ed/A and 55.8 lm/W, respectively, with warm white CIE coordinates of （0.34, 0.43）. The excellent efficiency and adaptive CIE coordi- nates are attributed to the mixed interlayer with improved charge carrier balance, optimized exciton distribution, and enhanced harvesting of singlet and triplet excitons.
基金supported by the Natural Science Foundation of China(22203042,21873048 and 22173044)。
文摘Two-dimensional(2D) semiconductors have captured broad interest as light emitters, due to their unique excitonic effects. These layer-blocks can be integrated through van der Waals assembly, i.e., fabricating homo-or heterojunctions, which show novel emission properties caused by interface engineering. In this review, we will first give an overview of the basic strategies that have been employed in interface engineering, including changing components, adjusting interlayer gap, and tuning twist angle. By modifying the interfacial factors, novel emission properties of emerging excitons are unveiled and discussed. Generally, well-tailored interfacial energy transfer and charge transfer within a 2D heterostructure cause static modulation of the brightness of intralayer excitons. As a special case, dynamically correlated dual-color emission in weakly-coupled bilayers will be introduced, which originates from intermittent interlayer charge transfer. For homobilayers and type Ⅱ heterobilayers, interlayer excitons with electrons and holes residing in neighboring layers are another important topic in this review. Moreover, the overlap of two crystal lattices forms moiré patterns with a relatively large period, taking effect on intralayer and interlayer excitons. Particularly, theoretical and experimental progresses on spatially modulated moiré excitons with ultra-sharp linewidth and quantum emission properties will be highlighted. Moiré quantum emitter provides uniform and integratable arrays of single photon emitters that are previously inaccessible, which is essential in quantum many-body simulation and quantum information processing. Benefiting from the optically addressable spin and valley indices, 2D heterostructures have become an indispensable platform for investigating exciton physics, designing and integrating novel concept emitters.
基金support from the National Natural Science Foundation of China(Nos.61775241,62090035,and U19A2090)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20180307151237242)+5 种基金Hunan Province Key Research and Development Project(No.2019GK2233)Hunan Provincial Science Fund for Distinguished Young Scholars(No,2020JJ2059)the Key Program of Science and Technology Department of Hunan Province(Nos.2019XK2001 and 2020XK2001)the Youth Innovation Team(No,2019012)of Central South UniversityThe authors are also thankful for the 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,No.DP180102976).
文摘Van der Waals heterostructures have recently emerged,in which two distinct transitional metal dichalcogenide(TMD)monolayers are stacked vertically to generate interlayer excitons(IXs),offing new opportunites for the design of optoelectronic devices.However,the bilayer heterostructure with type-II band alignment can only produce low quantum yield.Here,we present the observation of interlayer neutral excitons and trions in the MoSe_(2)/MoS_(2)/MoSe_(2)trilayer heterostructure(Tri-HS).In comparison to the 8 K bilayer heterostructure,the addition of a MoSe_(2)layer to the Tri-HS can significantly increase the quantum yield of IXs.It is believed the two symmetrical type-II band alignments formed in the Tri-HS could effectively promote the IX radiation recombination.By analyzing the photoluminescence(PL)spectrum of the IXs at cryogenic temperature and the power dependence,the existence of the interlayer trions was confirmed.Our results provide a promising platform for the development of more efficient optoelectronic devices and the investigation of new physical properties of TMDs.
基金the National Key Research and Development Program of China(Grant No.2020YFA0309604)the National Natural Science Foundation of China(Grant Nos.11834017,61888102,and 12074413)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0101340001)the Research Program of Beijing Academy of Quantum Information Sciences(Grant No.Y18G11).
文摘Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91850116,51772084,52022029,and U19A2090)Hunan Provincial Natural Science Foundation of China(Grant Nos.2018RS3051 and 2018WK4004)the Key Program of the Hunan Provincial Science and Technology Department,China(Grant No.2019XK2001).
文摘Due to the large exciton binding energy,two-dimensional(2D)transition metal dichalcogenides(TMDCs)provide an ideal platform for studying excitonic states and related photonics and optoelectronics.Polarization states lead to distinct light-matter interactions which are of great importance for device applications.In this work,we study polarized photoluminescence spectra from intralayer exciton and indirect exciton in WS_(2) and WSe_(2) atomic layers,and interlayer exciton in WS_(2)/WSe_(2) heterostructures by radially and azimuthally polarized cylindrical vector laser beams.We demonstrated the same in-plane and out-of-plane polarization behavior from the intralayer and indirect exciton.Moreover,with these two laser modes,we obtained interlayer exciton in WS_(2)/WSe_(2) heterostructures with stronger out-of-plane polarization,due to the formation of vertical electric dipole moment.
基金support from the National Natural Science Foundation of China(Nos.61874074,62004128,11974088)Science and Technology Project of Shenzhen(No.JCYJ20220531100815034)+1 种基金support from China Postdoctoral Science Foundation(No.2020M682847)Guangdong Basic and Applied Basic Research Foundation(General Program,No.2022A1515012055).
文摘Stacking single layers of atoms on top of each other provides a fundamental way to achieve novel material systems and engineer their physical properties,which offers opportunities for exploring fundamental physics and realizing next-generation optoelectronic devices.Among the two-dimensional(2D)-stacked systems,transition metal dichalcogenide(TMDC)heterostructures are particularly attractive because they host tightly-bonded interlayer excitons which possess various novel and appealing properties.These interlayer excitons have drawn significant research attention and hold high potential for the application in unique optoelectronic devices,such as polarization-and wavelength-tunable single photon emitters,valley Hall transistors,and possible high-temperature superconductors.The development of these devices requires a comprehensive understanding of the fundamental properties of these interlayer excitons and the impact of electric fields on their behaviors.In this review,we summarize the recent advances on the understanding of interlayer exciton dynamics under electric fields in TMDC heterostructures.We put emphasis on the electrical modulation of interlayer excitons’emission,the valley Hall transport of charge carriers after the separation of interlayer excitons by an electric field,and the correlation physics of interlayer excitons and charges under electrical doping and tuning.Challenges and perspectives are finally discussed for the application of TMDC heterostructures in future optoelectronics.
基金the National Natural Science Foundation of China(No.61775241)Hunan province key research and development project(No.2019GK2233)+5 种基金the Hunan Science Fund for Distinguished Young Scholar(No.2020JJ2059)Youth Innovation Team of Central South University(No.2019012)Hunan Province Graduate Research and Innovation Project(No.CX20190177)the Science and Technology Innovation Basic Research Project of Shenzhen(No.JCYJ20180307151237242)Also,Y.P.L.acknowledges the support provided by the Central South University of the State Key Laboratory of High-Performance Complex Manufacturing Project(No.ZZYJKT2020-12)Z.W.L.thanks the funding support from the Australian Research Council(ARC Discovery Projects)(Nos.DP210103539 and DP180102976).
文摘Interlayer excitons(IXS)are electron–hole pairs bound in the spatial separation layer by the Coulomb effect,and their lifetime is several orders of magnitude longer than that of direct excitons,providing an essential platform for long-lived exciton devices.The recent emergence of the van der Waals heterostructure(HS),which combines two layers of different transitional metal dichalcogenides(TMDs),has created new opportunities for IX research.Herein,we demonstrate the observation of double indirect interlayer excitons in the MoSe_(2)/WSe_(2)HS using photoluminescence(PL)spectroscopy.The intensities of the two peaks are essentially the same,and the energy difference is 22 meV,which is perfectly in line with the calculation result of density functional theory.Furthermore,the experience of variable excitation power also proves that the splitting of the IXs originates from the conduction band spin-splitting of MoSe_(2).The observation results provide a promising platform for further exploring the new physical properties and optoelectronic phenomena of TMD HS.
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 Key Research and Development Program of China(Grant No.2022YFB2803900)National Natural Science Foundation of China(Grant Nos.61704121,61974075)+2 种基金the Natural Science Foundation of Tianjin City(Grant Nos.19JCQNJC00700,22JCZDJC00460)the Scientific Research Project of Tianjin Municipal Education Commission(Grant No.2019KJ028)Fundamental Research Funds for the Central Universities of Nankai University(Grant No.22JCZDJC00460).
文摘Excitonic devices are an emerging class of technology that utilizes excitons as carriers for encoding, transmitting, and storing information. Van der Waals heterostructures based on transition metal dichalcogenides often exhibit a type II band alignment, which facilitates the generation of interlayer excitons. As a bonded pair of electrons and holes in the separation layer, interlayer excitons offer the chance to investigate exciton transport due to their intrinsic out-of-plane dipole moment and extended exciton lifetime. Furthermore, interlayer excitons can potentially analyze other encoding strategies for information processing beyond the conventional utilization of spin and charge. The review provided valuable insights and recommendations for researchers studying interlayer excitonic devices within van der Waals heterostructures based on transition metal dichalcogenides. Firstly, we provide an overview of the essential attributes of transition metal dichalcogenide materials, focusing on their fundamental properties, excitonic effects, and the distinctive features exhibited by interlayer excitons in van der Waals heterostructures. Subsequently, this discourse emphasizes the recent advancements in interlayer excitonic devices founded on van der Waals heterostructures, with specific attention is given to the utilization of valley electronics for information processing, employing the valley index. In conclusion, this paper examines the potential and current challenges associated with excitonic devices.
基金the financial support from the Singapore National Research Foundation through its Competitive Research Program(CRP Award No.NRF-CRP21-2018-0007)Singapore Ministry of Education(MOE2016-T2-2-077,MOE2016-T2-1-163 and MOE2016-T3-1-006(S))A^(*)Star QTE programme.
文摘The development of information processing devices with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and two-dimensional (2D) heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-orbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given.
基金the National Key Research and Development Program of China(2021YFA1200800).
文摘Two-dimensional transition metal dichalcogenides(TMDCs)have been regarded as an intriguing platform for exploring novel physical phenomena and optoelectronic devices due to their excitonic emission characteristics derived from the atomic thin thickness and reduced dielectric screening effect.Notably,monolayer TMDCs with a direct bandgap exhibiting strong photoluminescence(PL)are promising candidates for the light-emitting devices,while the interlayer excitons in heterostructures hold great potential for the photonic chips and optical communication applications.However,the non-ideal photoluminescent intensity and quality due to the ultrathin thickness and high defect density of experimentally obtained monolayer TMDCs limit the further development for the light-emission applications.Here,we summarize the research progress on the PL manipulation of the excitonic emission in TMDCs,where the PL intensity enhancement and emission wavelength regulation are included.The concept and characteristics of excitons are overviewed firstly,followed by the discussion on the evaluation and characterization of excitonic emission.The state-of-the-art progress on the manipulation of the neutral excitons and interlayer excitons PL are then summarized.Finally,the challenges and prospects are proposed.
基金primarily supported by the US Department of Energy,Office of Basic Energy Sciences under award number DE-SC0022082support from National Science Foundation under award number 2143568-DMR.
文摘Photoinduced interfacial charge transfer plays a critical role in energy conversion involving van der Waals(vdW)heterostructures constructed of inorganic nanostructures and organic materials.However,the effect of molecular stacking configurations on charge transfer dynamics is less understood.In this study,we demonstrated the tunability of interfacial charge separation in a type-Ⅱ heterojunction between monolayer(ML)WS_(2) and an organic semiconducting molecule[2-(3″′,4′-dimethyl-[2,2′:5′,2′:5″,2″′-quaterthiophen]-5-yl)ethan-1-ammonium halide(4Tm)]by rational design of relative stacking configurations.The assembly between ML-WS_(2) and the 4Tm molecule forms a face-to-face stacking when 4Tm molecules are in a selfaggregation state.In contrast,a face-to-edge stacking is observed when 4Tm molecule is incorporated into a 2D organic-inorganic hybrid perovskite lattice.The face-to-face stacking was proved to be more favorable for hole transfer from WS_(2) to 4Tm and led to interlayer excitons(IEs)emission.Transient absorption measurements show that the hole transfer occurs on a time scale of 150 fs.On the other hand,the face-to-edge stacking resulted in much slower hole transfer without formation of IEs.This inefficient hole transfer occurs on a similar time scale as A exciton recombination in WS_(2),leading to the formation of negative trions.These investigations offer important fundamental insights into the charge transfer processes at organic−inorganic interfaces.
