Wang z, mak k f, zhao h and shan j 2014 tightly bound excitons in monolayer wse2 phys. Here, we report on highfield magnetophotoluminescence pl study of excitons in monolayer wse 2. Hill, albert rigosi, yilei li, ozgur burak aslan, david r. Exciton binding energy and excited states in monolayers of tungsten diselenide wse2 are investigated using the combined linear absorption and twophoton photoluminescence excitation spectroscopy. Jan 22, 2018 g 0 w 0 calculations combined with the bethesalpeter equation are used to predict the optical spectra and exciton binding energies 0. He k, kumar n, zhao l, wang z, mak k f, zhao h and shan j 2014 tightly bound excitons in monolayer wse2 phys. Monolayer transition metal dichalcogenides host excitons, bound electronhole pairs that play a pivotal role in optoelectronic applications relying on strong lightmatter interaction. Osa shedding light on excitons nature in monolayer quantum.
Excitons are injected with a pointlike spatial distribution using a tightly focused femtosecond pulse. Tightly bound excitons in monolayer wse2 by keliang he, nardeep kumar, liang zhao, zefang wang, kin fai mak, hui zhao and jie shan no static citation data no static citation data cite. Heinz1 and jie shan2 twodimensional 2d atomic crystals, such as graphene and transitionmetal dichalcogenides, have emerged as a new class of materials with remarkable physical properties1. Distinct photoluminescence and raman spectroscopy signatures. Jul 11, 2014 tightly bound excitons in monolayer wse2. Unlike other semiconductors and fewlayer tmdcs, electrons and holes in monolayer tmdcs are tightly bound together at the energy. Jan 25, 2018 this type of defects permits radiative recombination of bound neutral excitons, which can make the pl intensity as strong as the intrinsic excitation.
Observation of biexcitons in monolayer wse 2 nature physics. Excitondominant electroluminescence from a diode of. Measurement of high exciton binding energy in the monolayer. Three types of defectrelated quantum emitters in monolayer tungsten diselenide wse2 are observed, with different exciton gfactors of 2. Magnetospectroscopy of exciton rydberg states in a cvd grown.
Dissociation of twodimensional excitons in monolayer wse2. Strongly bound excitons in monolayer pts2 and ptse2. Observation of biexcitons in monolayer wse2 nature physics. Exciton binding energy and nonhydrogenic rydberg series in. As a result, excitons in tmdc mls can be tightly bound even at room temperature, producing strong light absorption and. Exciton binding energy and nonhydrogenic rydberg series in monolayer ws 2 alexey chernikov, timothy c. Dipolar interactions between localized interlayer excitons. In summary, we have measured the homogeneous linewidth of excitons and examined various linewidth broadening mechanisms in monolayer wse2. In this work, we present a density functional theory investigation of excitons in 2d wse2, where we compare results obtained by standard generalized gradient approximation gga methods including spinorbit coupling with those by hybrid density functionals. Here, we experimentally probed the dynamics of excitonic states in monolayer wse 2 by investigating the temperature and polarization dependent photoluminescence pl spectra. Here we report the spectroscopic identification in a monolayer mos 2 fieldeffect transistor of tightly bound negative trions, a quasiparticle composed of two electrons and a. Strong manybody coulomb interactions allow for bound two and threebody excitonic states to form in monolayer transition metal dichalcogenides, but. Exciton binding energy and excited states in monolayers of tungsten diselenide wse2 are investigated using the combined linear absorption and twophoton.
Here, we directly trace the ultrafast formation of excitons by monitoring the absolute densities of bound and unbound electronhole pairs in single monolayers of wse2 on a diamond substrate following femtosecond nonresonant optical excitation. Molecularbeam epitaxy of monolayer and bilayer wse2. We found that excitonexciton and exciton phonon interaction and population recombination to be the dominant mechanisms for quantum dephasing. A manifestation of these manybody interactions is the formation of excitons, bound electronhole pairs, but higherorder excitonic states are also. Probing the origin of excitonic states in monolayer wse 2 scientific. Monolayers of semiconducting transition metal dichalcogenides are two dimensional directgap systems which host tightly bound excitons with an internal degree of freedom corresponding to the.
Spatiotemporal dynamics of excitons in monolayer and bulk. Probing the origin of excitonic states in monolayer wse2. Enabling valley selective exciton scattering in monolayer wse. Exciton valley dynamics in monolayer wse2 probed by the two. Experimental evidence for dark excitons in monolayer wse 2 xiaoxiao zhang,1 yumeng you,1,2 shu yang frank zhao,3 and tony f. Here we report observation of 2s excited exciton levels in monolayer ws 2 and wse 2. Tightly bound trions in monolayer mos2 kin fai mak1, keliang he2, changgu lee3, gwan hyoung lee4, james hone4, tony f. Investigating the dynamics of excitons in monolayer wse2. Shan, tightly bound excitons in monolayer wse2, phys.
Measurement of the optical dielectric function of monolayer. The exciton dynamics in monolayer and bulk mose2 samples are studied by transient absorption microscopy with a high spatiotemporal resolution. Osa selfconsistent dielectric constant determination for. Four pronounced pl peaks were identified below a temperature of 60 k at nearresonant excitation and assigned to exciton, trion and localized states from excitation power. Probing and manipulating valley coherence of dark excitons in. Identifying defectrelated quantum emitters in monolayer wse2. Pdf strain tuning of excitons in monolayer wse2 researchgate. Due to the large photoluminescence quantum yield, high mobility and good stability, organic super acid treated twodimensional wse2 has drawn much attention.
Investigating the dynamics of excitons in monolayer wse2 before. The sample consists of a wse 2 monolayer encapsulated in hbn ref. Observation of biexcitons in monolayer wse2 request pdf. Strong roomtemperature emission from defect states in cvd. Exciton diffusion in monolayer and bulk mose2 nanoscale. Direct observation of ultrafast exciton formation in a. A optical image and b schematic cross section of an exfoliated wse 2 flake with monolayer 1l, bilayer 2l, and bulk regions partially capped with monolayer graphene g and supported by a graphite flake on a doped silicon substrate. Particularly attractive is the extraordinarily large oscillator strength as well as binding energy of the excitonic quasiparticles in these atomicallythin crystal lattices.
Here, the authors investigate the main exciton dissociation pathway in pn junctions of. The observation of both ground and excited states allows us to determine a lower bound for the exciton binding energy. It turns out that the excitons are strongly bound and therefore very stable against external perturbations. Sep 23, 2016 nature optical generation of excitonic valley coherence in monolayer wse2 1. Tightly bound excitons in monolayer wse 2 keliang he,1 nardeep kumar,2 liang zhao,1 zefang wang,1 kin fai mak,3 hui zhao,2 and jie shan1 1department of physics, case western reserve university, 10900 euclid avenue, cleveland, ohio 44106, usa 2department of physics and astronomy, the university of kansas, lawrence, kansas 66045, usa 3kavli institute at cornell for nanoscale science and. Download scientific diagram a representative pl spectra of monolayer wse 2 excited by femtosecond ir. These high binding energy excitons exhibit behavior similar to excited atoms, with energy levels designated 1s, 2s, 2p and so on. Strong manybody coulomb interactions allow for bound two and threebody excitonic states to form in monolayer transition metal dichalcogenides, but it is now shown that such interactions are. Jun 12, 2019 the results of magnetooptical spectroscopy investigations of excitons in a cvd grown monolayer of wse 2 encapsulated in hexagonal boron nitride are presented. This shows the hole transfer process since the hole transfer time is close to the. Distinct photoluminescence and raman spectroscopy signatures for identifying highly crystalline ws2 monolayers produced by different growth methods volume 31 issue 7 amber mccreary, ayse berkdemir, junjie wang, minh an nguyen, ana laura elias, nestor perealopez, kazunori fujisawa, bernd kabius, victor carozo, david a. Excitondominant electroluminescence from a diode of monolayer mos 2 yu ye, 1 ziliang ye,1 majid gharghi,1 hanyu zhu,1 mervin zhao,1,2 yuan wang,1 xiaobo yin,1,2 and xiang zhang1,2,a 1nsf nanoscale science and engineering center, university of california, 3112 etcheverry hall, berkeley, california 94720, usa. Frequencydependent dielectric constant dispersion of monolayer wse2. By tuning the probe photon energy in resonance with the free excitons and trions, the valley relaxation time of different excitonic states in monolayer wse 2 is determined.
Valley relaxation time of the free exciton in monolayer wse. In twodimensional semiconductors excitons are strongly bound, suppressing the creation of free carriers. Transient excitonpolariton dynamics in wse2 by ultrafast. Optical generation of excitonic valley coherence in monolayer wse2 aaron m. Nature optical generation of excitonic valley coherence in. Tightly bound excitons in monolayer wse 2 keliang he1, nardeep kumar2, liang zhao1, zefang wang1, kin fai mak3, hui zhao2, jie shan1 1department of physics, case western reserve university, 10900 euclid avenue, cleveland, ohio 44106, usa 2department of physics and astronomy, the university of kansas, lawrence, kansas 66045, usa 3kavli institute at cornell for nanoscale science and. Tightly bound trions in monolayer mos 2 nature materials. Mandrus3,4,6, di xiao7, wang yao2 and xiaodong xu1,5 as a consequence of degeneracies arising from crystal.
Radiatively limited dephasing and exciton dynamics in mose2. Here, we directly trace the ultrafast formation of excitons by monitoring the absolute densities of bound and unbound electron. Heinz4,5, 1departments of physics and electrical engineering, columbia university, 538 west 120th street. Intrinsic homogeneous linewidth and broadening mechanisms of. Although the monolayer ws 2 is not intentionally doped, the structural defects and substrate effects such as charge transfer and defects modulate the carrier density away from its insulating state. On the other hand, transition metal dichalcogenides tmds with chemical formula mx 2 m mo and w. Our findings reveal a new way to tailor the optical properties of twodimensional tmdcs without any additional processes performed after growth. Additionally, we observed a rapid decrease in the degree of circular polarization of the pl at increasing temperatures indicating a relatively strong electronphonon coupling and impurity. Photoluminescence properties and exciton dynamics in. Determination of band offsets, hybridization, and exciton. Probing and manipulating valley coherence of dark excitons in monolayer wse2. Monolayers of semiconducting transition metal dichalcogenides are twodimensional directgap systems which host tightly bound excitons with an internal degree of freedom corresponding to the.
Pdf microsecond valley lifetime of defectbound excitons. However, reports about the influence of organic super acid treatment on the dynamic processes of excitons of monolayer wse2 are still rare. Exciton binding energy and excited states in monolayers of tungsten diselenide wse2 are investigated using the combined linear. Radiatively limited dephasing and exciton dynamics in mose2 monolayers revealed with fourwave mixing microscopy. From this model, we estimated a lower bound of the exciton binding energy of 198 mev for monolayer wse2 and explained the vanishing of the localized states. Heinz, control of valley polarization in monolayer mos2 by optical helicity, nature nanotech. To confirm the origin of the side band around exciton a, we record the pl spectra of monolayer ws. He k1, kumar n2, zhao l1, wang z1, mak kf3, zhao h2, shan j1. Excitonpolaritons in multilayer wse2 in a planar microcavity.
Nature of excitons in bidimensional wse2 by hybrid density. As a member of tmdc materials, monolayer wse2 has a relatively high. Diploma in mathematics and physics, moscow state university 1996 m. Photoluminescence properties and exciton dynamics in monolayer wse 2 tengfei yan, xiaofen qiao, xiaona liu, pingheng tan, and xinhui zhanga state key laboratory of superlattices and microstructures, institute of semiconductors, chinese academy of. Threedimensional resonant exciton in monolayer tungsten. Probing the response of twodimensional crystals by optical spectroscopy. Tightly bound trions in monolayer mos2 stanford university. Observation of highenergy excitonic peaks in monolayer wse2. Enabling valley selective exciton scattering in monolayer. Here we report the spectroscopic identification in a monolayer mos 2 fieldeffect transistor of tightly bound negative trions, a quasiparticle composed of two electrons and a hole.
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