The exploration of novel chiral optical platforms holds both fundamental and practical importances,which have shown great promise towards applications in valleytronics,chiral sensing and nanoscopic chiroptics.In this ...The exploration of novel chiral optical platforms holds both fundamental and practical importances,which have shown great promise towards applications in valleytronics,chiral sensing and nanoscopic chiroptics.In this work,we combine two key concepts—chiral bound states in the continuum and exciton polaritons—to showcase a strong chiral response from polaritons.Using the finite element method,we numerically design a CsPbBr_(3)based metasurface that supports intrinsically chiral bound states in the continuum and verify the chirality by calculating the reflection spectrum and eigenpolarization mapping.We further demonstrate chirality-dependent exciton polariton angular dispersion arising from the strong coupling between the chiral BIC and excitons in CsPbBr_(3)by simulating the polariton angle-resolved absorption spectrum.Reciprocity analysis reveals that the polariton photoluminescence in different momentum space locations is selectively enhanced by chiral pumping light.Our results suggest a promising first step towards chiral polaritonics.展开更多
Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since ...Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief backgroundintroduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials(PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.展开更多
Semiconducting piezoelectricα-In_(2)Se_(3) and 3R MoS_(2) have attracted tremendous attention due to their unique electronic properties.Artificial van der Waals(vdWs)hetero-structures constructed withα-In_(2)Se_(3)a...Semiconducting piezoelectricα-In_(2)Se_(3) and 3R MoS_(2) have attracted tremendous attention due to their unique electronic properties.Artificial van der Waals(vdWs)hetero-structures constructed withα-In_(2)Se_(3)and 3R MoS_(2)flakes have shown promising applications in optoelectronics and photocatal-ysis.Here,we present the first flexibleα-In_(2)Se_(3)/3R MoS_(2)vdWs p-n heterojunction devices for photodetection from the visible to near infrared region.These heterojunction devices exhibit an ultrahigh photoresponsivity of 2.9×10^(3)A W^(−1) and a substantial specific detectivity of 6.2×10^(10) Jones under a compressive strain of−0.26%.The photocurrent can be increased by 64%under a tensile strain of+0.35%,due to the heterojunction energy band modulation by piezoelectric polarization charges at the hetero-junction interface.This work demonstrates a feasible approach to enhancement of α-In_(2)Se_(3)/3R MoS_(2) photoelectric response through an appropriate mechanical stimulus.展开更多
Monolayer group VI transition metal dichalcogenides(TMDs)have recently emerged as promising candidates for photonic and opto-valleytronic applications.The optoelectronic properties of these atomically-thin semiconduct...Monolayer group VI transition metal dichalcogenides(TMDs)have recently emerged as promising candidates for photonic and opto-valleytronic applications.The optoelectronic properties of these atomically-thin semiconducting crystals are strongly governed by the tightly bound electron-hole pairs such as excitons and trions(charged excitons).The anomalous spin and valley configurations at the conduction band edges in monolayer WS_(2)give rise to even more fascinating valley many-body complexes.Here we find that the indirect Q valley in the first Brillouin zone of monolayer WS_(2)plays a critical role in the formation of a new excitonic state,which has not been well studied.By employing a high-quality h-BN encapsulated WS_(2)field-effect transistor,we are able to switch the electron concentration within K-Q valleys at conduction band edges.Consequently,a distinct emission feature could be excited at the high electron doping region.Such feature has a competing population with the K valley trion,and experiences nonlinear power-law response and lifetime dynamics under doping.Our findings open up a new avenue for the study of valley many-body physics and quantum optics in semiconducting 2D materials,as well as provide a promising way of valley manipulation for next-generation entangled photonic devices.展开更多
The year 2022 marks the 30^(th)anniversary of Chinese Physics B.This editorial provides a brief history of the journal and introduces the anniversary theme collection comprising over 30 invited reviews and perspective...The year 2022 marks the 30^(th)anniversary of Chinese Physics B.This editorial provides a brief history of the journal and introduces the anniversary theme collection comprising over 30 invited reviews and perspective articles from renowned scholars in various branches of physics.展开更多
In recent years,two-dimensional(2D)van der Waals materials have emerged as a focal point in materials research,drawing increasing attention due to their potential for isolating and synergistically combining diverse at...In recent years,two-dimensional(2D)van der Waals materials have emerged as a focal point in materials research,drawing increasing attention due to their potential for isolating and synergistically combining diverse atomic layers.Atomically thin transition metal dichalcogenides(TMDs)are one of the most alluring van der Waals materials owing to their exceptional electronic and optical properties.The tightly bound excitons with giant oscillator strength render TMDs an ideal platform to investigate strong light-matter coupling when they are integrated with optical cavities,providing a wide range of possibilities for exploring novel polaritonic physics and devices.In this review,we focused on recent advances in TMD-based strong light-matter coupling.In the foremost position,we discuss the various optical structures strongly coupled to TMD materials,such as Fabry-Perot cavities,photonic crystals,and plasmonic nanocavities.We then present several intriguing properties and relevant device applications of TMD polaritons.In the end,we delineate promising future directions for the study of strong light-matter coupling in van der Waals materials.展开更多
We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismu...We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between ＂layers＂, while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials （MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus）, including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories： phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.展开更多
Chirality, which describes the broken mirror symmetry in geometric structures, exists macroscopically in our daily life as well as microscopically down to molecular levels. Correspondingly, chiral molecules interact d...Chirality, which describes the broken mirror symmetry in geometric structures, exists macroscopically in our daily life as well as microscopically down to molecular levels. Correspondingly, chiral molecules interact differently with circularly polarized light exhibiting opposite handedness(left-handed and right-handed). However, the interaction between chiral molecules and chiral light is very weak. In contrast, artificial chiral plasmonic structures can generate "super-chiral" plasmonic near-field, leading to enhanced chiral light-matter(or chiroptical) interactions. The "super-chiral" near-field presents different amplitude and phase under opposite handedness incidence, which can be utilized to engineer linear and nonlinear chiroptical interactions. Specifically,in the interaction between quantum emitters and chiral plasmonic structures, the chiral hot spots can favour the emission with a specific handedness. This article reviews the state-of-the-art research on the design, fabrication and chiroptical response of different chiral plasmonic nanostructures or metasurfaces. This review also discusses enhanced chiral light-matter interactions that are essential for applications like chirality sensing, chiral selective light emitting and harvesting. In the final part, the review ends with a perspective on future directions of chiral plasmonics.展开更多
Up-conversion photoluminescence(UCPL)refers to the elementary process where low-energy photons are converted into high-energy ones via consecutive interactions inside a medium.When additional energy is provided by int...Up-conversion photoluminescence(UCPL)refers to the elementary process where low-energy photons are converted into high-energy ones via consecutive interactions inside a medium.When additional energy is provided by intermnal thermal energy in the form of lttice vibrations(phonons),the process is called phonon-assisted UCPL.Here,we report the exceptionally large phonon-assisted energy gain of up to^8kgT(kg is Boltzmann constant,T is temperature)on all-inorganic lead halide perovskite semiconductor colloidal nanocrystals that goes beyond the maximum capabilty of only harvesting optical phonon modes.By systematic optical study in combination with a statistical probability model,we explained the nontrivial phonon-assisted UCPL process in perovskites nanocrystals,where in addition to the strong electron-phonon(light-matter)coupling,other nonlinear processes such as phonon-phonon(matter-matter)interaction also effectively boost the up-conversion efficiency.展开更多
Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-e...Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-electrons result in inadequate quantum yields,especially in the mid-infrared range.Here,we report a macroscopic assembled graphene(nMAG)nanofilm/silicon heterojunction for ultrafast mid-infrared photodetection.The assembled Schottky diode works in 1.5-4.0μm at room temperature with fast response(20-30 ns,rising time,4 mm2 window)and high detectivity(1.61011 to 1.9109 Jones from 1.5 to 4.0μm)under the pulsed laser,outperforming single-layer-graphene/silicon photodetectors by 2-8 orders.These performances are attributed to the greatly enhanced photo-thermionic effect of electrons in nMAG due to its high light absorption(~40%),long carrier relaxation time(~20 ps),low work function(4.52 eV),and suppressed carrier number fluctuation.The nMAG provides a long-range platform to understand the hot-carrier dynamics in bulk 2D materials,leading to broadband and ultrafast MIR active imaging devices at room temperature.展开更多
Exciton-polariton condensation is regarded as a spontaneous macroscopic quantum phenomenon with phase ordering and collective coherence.By engineering artificial annular potential landscapes in halide perovskite semic...Exciton-polariton condensation is regarded as a spontaneous macroscopic quantum phenomenon with phase ordering and collective coherence.By engineering artificial annular potential landscapes in halide perovskite semiconductor microcavities,we experimentally and theoretically demonstrate the room-temperature spontaneous formation of a coherent superposition of exciton-polariton orbital states with symmetric petal-shaped patterns in real space,resulting from symmetry breaking due to the anisotropic effective potential of the birefringent perovskite crystals.The lobe numbers of such petal-shaped polariton condensates can be precisely controlled by tuning the annular potential geometry.These petal-shaped condensates form in multiple orbital states,carrying locked alternating nphase shifts and vortex-anti vortex superposition cores,arising from the coupling of counterrotating exciton-polaritons in the confined circular waveguide.Our geometrically patterned microcavity exhibits promise for realizing room-temperature topological polaritonic devices and optical polaritonic switches based on periodic annular potentials.展开更多
Van der Waals heterojunctions are fast-emerging quantum structures fabricated by the controlled stacking of two-dimensional(2D)materials.Owing to the atomically thin thickness,their carrier properties are not only det...Van der Waals heterojunctions are fast-emerging quantum structures fabricated by the controlled stacking of two-dimensional(2D)materials.Owing to the atomically thin thickness,their carrier properties are not only determined by the host material itself,but also defined by the interlayer interactions,including dielectric environment,charge trapping centers,and stacking angles.The abundant constituents without the limitation of lattice constant matching enable fascinating electrical,optical,and magnetic properties in van der Waals heterojunctions toward next-generation devices in photonics,optoelectronics,and information sciences.This review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides(TMDCs),a family of quantum materials with strong excitonic effects and unique valley properties,and other related 2D materials such as graphene and hexagonalboron nitride.In the first part,we summarize the ultrafast charge transfer processes in van der Waals heterojunctions,including its experimental evidence and theoretical understanding,the interlayer excitons at the TMDC interfaces,and the hot carrier injection at the graphene/TMDCs interface.In the second part,the energy transfer,including both Förster and Dexter types,are reviewed from both experimental and theoretical perspectives.Finally,we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field.展开更多
We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has be...We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.展开更多
Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications....Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications.Here,we investigated the carrier dynamics and many-body interactions in two-dimensional(2D)transition metal dichalcogenides(TMDs),using monolayer WS2 as an example,by employing femtosecond broadband pump-probe spectroscopy.Three time regimes for the exciton energy renormalization are unambiguously revealed with a distinct red-blue-red shift upon above-bandgap optical excitations.We attribute the dominant physical process in the three typical regimes to free carrier screening effect,Coulombic exciton-exciton interactions and Auger photocarrier generation,respectively,which show distinct dependence on the optical excitation wavelength,pump fluences and/or lattice temperature.An intrinsic exciton radiative lifetime of about 1.2 picoseconds(ps)in monolayer WS2 is unraveled at low temperature,and surprisingly the efficient Auger nonradiative decay of both bright and dark excitons puts the system in a nonequilibrium state at the nanosecond timescale.In addition,the dynamics of trions at low temperature is observed to be significantly different from that of excitons,e.g.,a long radiative lifetime of^108.7 ps at low excitation densities and the evolution of trion energy as a function of delay times.Our findings elucidate the dynamics of excitonic quasiparticles and the intricate many-body physics in 2D semiconductors,underpinning the future development of photonics,valleytronics and optoelectronics based on 2D semiconductors.展开更多
The much slower progress in enhancing the thermoelectric performance of n-type Bi2Te3 than that of p-type Bi2Te3 based materials in the past decade hinders the widespread use in power generation and refrigeration. Her...The much slower progress in enhancing the thermoelectric performance of n-type Bi2Te3 than that of p-type Bi2Te3 based materials in the past decade hinders the widespread use in power generation and refrigeration. Here, a facile bottom-up solution-synthesis with spark plasma sintering(SPS) process has been developed to build n-type Bi2Te3-xSex bulk nanocomposites, which substantially improves the power factor and decreases the lattice thermal conductivity by tuning the interface scattering of phonons and electrons. The stoichiometric composition in ternary Bi2Te3-xSex nanocomposites is also tuned to optimize the carrier concentration and lattice thermal conductivity. The optimized bulk nanocomposite Bi2Te2.7Se0.3 exhibits a ZT of 1.1 at^371 K, which is comparable to the corresponding commercially available ingots. Our results demonstrate the great potential of the solution-processed n-type Bi2Te3-xSex nanocomposites for cost-effective thermoelectric applications.展开更多
The exciting progress in graphene research in the past 15 years[1,2] has further stimulated the exploration of other non-graphene two-dimensional (2D) materials [3], such as h-BN [4,5], transitional metal dichalcogeni...The exciting progress in graphene research in the past 15 years[1,2] has further stimulated the exploration of other non-graphene two-dimensional (2D) materials [3], such as h-BN [4,5], transitional metal dichalcogenides (TMDs)[6,7], black phosphorene [8],etc. Research on these ultimately atomic thin 2D materials has grown exponentially owning to their fascinating properties and enormous potential in the fields of physics, chemistry, optics and photonics, material sciences, medicine and engineering.展开更多
Introducing magnetic dopants into twodimensional transition metal dichalcogenides has recently attracted considerable attention due to its promising applications in spintronics and valleytronics.Herein we realized man...Introducing magnetic dopants into twodimensional transition metal dichalcogenides has recently attracted considerable attention due to its promising applications in spintronics and valleytronics.Herein we realized manganese-doped molybdenum diselenide(MoSe_(2))single crystal via chemical vapor transport(CVT)reaction,containing up to 2.9%(atomic concentration)Mn dopants,and investigated the light-matter interaction in these samples.We observed a suppressed trion intensity,a longer photoluminescence lifetime,and prominent blue-and red-shift of E_(2g)^(2)(in-plane)and A_(1g)(out-of-plane)Raman modes,respectively.Moreover,the Mn dopants increase the valley Zeeman splitting of the MoSe_(2) monolayer by~50%,while preserving the linear dependence on magnetic field.First-principles calculations indicate that the spin-polarized deep level defect states are formed due to the Mn substitutional dopants in the Mo Se_(2) lattice.The resulting defect potential favors the funnelling of excitons towards the defects.The Mn dopants reduce the magnitude of the interatomic force constants,explaining the red-shift of the A_(1g)mode.The Mn atoms and their immediate Mo and Se neighbors carry significant magnetic moments,which enhance the observed exciton g-factors due to the exchange interactions affecting defect-bound excitons.展开更多
Exciton polaritons in atomically thin transition-metal dichalcogenide microcavities provide a versatile platform for advancing optoelectronic devices and studying the interacting Bosonic physics at ambient conditions....Exciton polaritons in atomically thin transition-metal dichalcogenide microcavities provide a versatile platform for advancing optoelectronic devices and studying the interacting Bosonic physics at ambient conditions.Rationally engineering the favorable properties of polaritons is critically required for the rapidly growing research.Here,we demonstrate the manipulation of nonlinear polaritons with the lithographically defined potential landscapes in monolayer WS_(2)microcavities.The discretization of photoluminescence dispersions and spatially confined patterns indicate the deterministic on-site localization of polaritons by the artificial mesa cavities.Varying the trapping sizes,the polariton-reservoir interaction strength is enhanced by about six times through managing the polariton–exciton spatial overlap.Meanwhile,the coherence of trapped polaritons is significantly improved due to the spectral narrowing and tailored in a picosecond range.Therefore,our work not only offers a convenient approach to manipulating the nonlinearity and coherence of polaritons but also opens up possibilities for exploring many-body phenomena and developing novel polaritonic devices based on 2D materials.展开更多
Halide perovskite semiconductors have emerged as promising candidates for the next-generation low-energy consumption,high-flexibility photonics and optoelectronic devices thanks to their superior optical and excitonic...Halide perovskite semiconductors have emerged as promising candidates for the next-generation low-energy consumption,high-flexibility photonics and optoelectronic devices thanks to their superior optical and excitonic properties as well as fabrication convenience.This special issue,including three review papers and six original research papers,focuses on the studies of both fundamentals and applications of perovskite photonics,covering materials,excitonic properties,nonlinear optics,strong light–matter interactions,and optoelectronic devices.展开更多
The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study,...The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.展开更多
基金funding support from the National Key Research and Development Program of China(Grant No.2022YFA1204700)the National Natural Science Foundation of China(Grant Nos.12020101003,92056204,and 92250301)the funding support from the National Natural Science Foundation of China(Grant No.12274034)。
文摘The exploration of novel chiral optical platforms holds both fundamental and practical importances,which have shown great promise towards applications in valleytronics,chiral sensing and nanoscopic chiroptics.In this work,we combine two key concepts—chiral bound states in the continuum and exciton polaritons—to showcase a strong chiral response from polaritons.Using the finite element method,we numerically design a CsPbBr_(3)based metasurface that supports intrinsically chiral bound states in the continuum and verify the chirality by calculating the reflection spectrum and eigenpolarization mapping.We further demonstrate chirality-dependent exciton polariton angular dispersion arising from the strong coupling between the chiral BIC and excitons in CsPbBr_(3)by simulating the polariton angle-resolved absorption spectrum.Reciprocity analysis reveals that the polariton photoluminescence in different momentum space locations is selectively enhanced by chiral pumping light.Our results suggest a promising first step towards chiral polaritonics.
文摘Research on two-dimensional(2D) materials has been explosively increasing in last seventeen years in varying subjects including condensed matter physics, electronic engineering, materials science, and chemistry since the mechanical exfoliation of graphene in 2004. Starting from graphene, 2D materials now have become a big family with numerous members and diverse categories. The unique structural features and physicochemical properties of 2D materials make them one class of the most appealing candidates for a wide range of potential applications. In particular, we have seen some major breakthroughs made in the field of 2D materials in last five years not only in developing novel synthetic methods and exploring new structures/properties but also in identifying innovative applications and pushing forward commercialisation. In this review, we provide a critical summary on the recent progress made in the field of 2D materials with a particular focus on last five years. After a brief backgroundintroduction, we first discuss the major synthetic methods for 2D materials, including the mechanical exfoliation, liquid exfoliation, vapor phase deposition, and wet-chemical synthesis as well as phase engineering of 2D materials belonging to the field of phase engineering of nanomaterials(PEN). We then introduce the superconducting/optical/magnetic properties and chirality of 2D materials along with newly emerging magic angle 2D superlattices. Following that, the promising applications of 2D materials in electronics, optoelectronics, catalysis, energy storage, solar cells, biomedicine, sensors, environments, etc. are described sequentially. Thereafter, we present the theoretic calculations and simulations of 2D materials. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future outlooks in this rapidly developing field.
基金MOE AcRF Tier2(2018-T2-2-005),MOE AcRF Tier1(2018-T1-005-001)A^(*)STAR AME IRG Grant SERC A1983c0027,Singapore.
文摘Semiconducting piezoelectricα-In_(2)Se_(3) and 3R MoS_(2) have attracted tremendous attention due to their unique electronic properties.Artificial van der Waals(vdWs)hetero-structures constructed withα-In_(2)Se_(3)and 3R MoS_(2)flakes have shown promising applications in optoelectronics and photocatal-ysis.Here,we present the first flexibleα-In_(2)Se_(3)/3R MoS_(2)vdWs p-n heterojunction devices for photodetection from the visible to near infrared region.These heterojunction devices exhibit an ultrahigh photoresponsivity of 2.9×10^(3)A W^(−1) and a substantial specific detectivity of 6.2×10^(10) Jones under a compressive strain of−0.26%.The photocurrent can be increased by 64%under a tensile strain of+0.35%,due to the heterojunction energy band modulation by piezoelectric polarization charges at the hetero-junction interface.This work demonstrates a feasible approach to enhancement of α-In_(2)Se_(3)/3R MoS_(2) photoelectric response through an appropriate mechanical stimulus.
基金the strong support from Singapore Ministry of Education via AcRF Tier 3 Programme “Geometrical Quantum Materials” (MOE2018-T3-1-002)AcRF Tier 2 grants (MOE2017-T2-1040)+7 种基金the National Natural Science Foundation of China (Grant No. 61435010)the National Natural Science Foundation of China (Grant No. 61905156)the National Natural Science Foundation of China (Grant No. 61575010)the China Postdoctoral Science Foundation (Grant No. 2017M622764)the Natural Science Foundation of Fujian Province (Grant No. 2022J01555)the Beijing Municipal Natural Science Foundation (Grant No. 4162016)the financial support of the Presidential Postdoctoral Fellowship program of the Nanyang Technological Universitysupport from the Elemental Strategy Initiative conducted by the MEXT, Japan and the CREST (JPMJCR15F3), JST
文摘Monolayer group VI transition metal dichalcogenides(TMDs)have recently emerged as promising candidates for photonic and opto-valleytronic applications.The optoelectronic properties of these atomically-thin semiconducting crystals are strongly governed by the tightly bound electron-hole pairs such as excitons and trions(charged excitons).The anomalous spin and valley configurations at the conduction band edges in monolayer WS_(2)give rise to even more fascinating valley many-body complexes.Here we find that the indirect Q valley in the first Brillouin zone of monolayer WS_(2)plays a critical role in the formation of a new excitonic state,which has not been well studied.By employing a high-quality h-BN encapsulated WS_(2)field-effect transistor,we are able to switch the electron concentration within K-Q valleys at conduction band edges.Consequently,a distinct emission feature could be excited at the high electron doping region.Such feature has a competing population with the K valley trion,and experiences nonlinear power-law response and lifetime dynamics under doping.Our findings open up a new avenue for the study of valley many-body physics and quantum optics in semiconducting 2D materials,as well as provide a promising way of valley manipulation for next-generation entangled photonic devices.
文摘The year 2022 marks the 30^(th)anniversary of Chinese Physics B.This editorial provides a brief history of the journal and introduces the anniversary theme collection comprising over 30 invited reviews and perspective articles from renowned scholars in various branches of physics.
基金Q.X.gratefully acknowledges the following funding sources:National Key Research and Development Program of China(Grant no.2022YFA1204700)National Natural Science Foundation of China(Grant no.12250710126)+2 种基金funding support from the State Key Laboratory of Low-Dimensional Quantum Physics of Tsinghua University and the Tsinghua University Initiative Scientific Research Program.J.Z and T.L.gratefully acknowledge support from the Singapore Ministry of Education via the AcRF Tier 3 Program"Geometrical Quantum Materials"(MOE2018-T3-1-002)S.G.gratefully acknowledges funding support from the National Natural Science Foundation of China(Grant No.12274034)the start-up grant from the Beijing Academy of Quantum Information Sciences.
文摘In recent years,two-dimensional(2D)van der Waals materials have emerged as a focal point in materials research,drawing increasing attention due to their potential for isolating and synergistically combining diverse atomic layers.Atomically thin transition metal dichalcogenides(TMDs)are one of the most alluring van der Waals materials owing to their exceptional electronic and optical properties.The tightly bound excitons with giant oscillator strength render TMDs an ideal platform to investigate strong light-matter coupling when they are integrated with optical cavities,providing a wide range of possibilities for exploring novel polaritonic physics and devices.In this review,we focused on recent advances in TMD-based strong light-matter coupling.In the foremost position,we discuss the various optical structures strongly coupled to TMD materials,such as Fabry-Perot cavities,photonic crystals,and plasmonic nanocavities.We then present several intriguing properties and relevant device applications of TMD polaritons.In the end,we delineate promising future directions for the study of strong light-matter coupling in van der Waals materials.
基金Q. H. X. gratefully thanks Singapore National Research Foundation via a Fellowship grant （No. NRF-RF2009-06） and an Investigatorship grant （No. NRF-NRFI2015-03）, Ministry of Education via a tier2 grant （No. MOE2012-T2-2-086） and a tier1 grant （No. 2013-T1-002-232）. S. Y. Q. and X. Luo gratefully acknowledge the Singapore National Research Foun- dation （NRF） for funding under the NRF Fellowship （No. NRF-NRFF2013-07）. Z. J. gratefully thanks National Natural Science Foundation of China （Nos. 11574305 and 51527901） and financial support from the National 1000 Talent Plan of China via a Young Project. The computations were performed on the cluster of NUS Graphene Research Centre. S. Y. Q. and X. Luo acknowledge the National Research Foundation, Prime Minister＇s Office, Singapore, under its Medium Sized Centre Programme.
文摘We review lattice vibrational modes in atomically thin two-dimensional （2D） layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between ＂layers＂, while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials （MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus）, including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories： phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.
基金the Singapore National Research Foundation-Agence Nationale de la Recherche(Grant No.NRF2017-NRF-ANR0052DCHIRAL).
文摘Chirality, which describes the broken mirror symmetry in geometric structures, exists macroscopically in our daily life as well as microscopically down to molecular levels. Correspondingly, chiral molecules interact differently with circularly polarized light exhibiting opposite handedness(left-handed and right-handed). However, the interaction between chiral molecules and chiral light is very weak. In contrast, artificial chiral plasmonic structures can generate "super-chiral" plasmonic near-field, leading to enhanced chiral light-matter(or chiroptical) interactions. The "super-chiral" near-field presents different amplitude and phase under opposite handedness incidence, which can be utilized to engineer linear and nonlinear chiroptical interactions. Specifically,in the interaction between quantum emitters and chiral plasmonic structures, the chiral hot spots can favour the emission with a specific handedness. This article reviews the state-of-the-art research on the design, fabrication and chiroptical response of different chiral plasmonic nanostructures or metasurfaces. This review also discusses enhanced chiral light-matter interactions that are essential for applications like chirality sensing, chiral selective light emitting and harvesting. In the final part, the review ends with a perspective on future directions of chiral plasmonics.
基金the Singapore National Research Foundation through the NRF Investigatorship Award(No.NRF-NRFI2015-03)the Singapore Ministry of Education via AcRF Tier 3 Programme(No.MOE2018-T3-1-002),Tier 2 grant(No.MOE2018-T2-2-068)and Tier 1 grants(Nos.RG103/15 and RG113/16)A.G.D.A.gratefully acknowledges the financial support of the Presidential Postdoctoral Fellowship program of the Nanyang Technological University
文摘Up-conversion photoluminescence(UCPL)refers to the elementary process where low-energy photons are converted into high-energy ones via consecutive interactions inside a medium.When additional energy is provided by intermnal thermal energy in the form of lttice vibrations(phonons),the process is called phonon-assisted UCPL.Here,we report the exceptionally large phonon-assisted energy gain of up to^8kgT(kg is Boltzmann constant,T is temperature)on all-inorganic lead halide perovskite semiconductor colloidal nanocrystals that goes beyond the maximum capabilty of only harvesting optical phonon modes.By systematic optical study in combination with a statistical probability model,we explained the nontrivial phonon-assisted UCPL process in perovskites nanocrystals,where in addition to the strong electron-phonon(light-matter)coupling,other nonlinear processes such as phonon-phonon(matter-matter)interaction also effectively boost the up-conversion efficiency.
基金National Natural Science Foundation of China,Grant/Award Numbers:52090030,51973191,92164106,61874094China Postdoctoral Science Foundation,Grant/Award Number:2020M681819+2 种基金Fundamental Research Funds for the Central Universities,Grant/Award Numbers:K20200060,2021FZZX001-17Key Laboratory of Novel Adsorption and Separation Materials and Application Technology of Zhejiang Province,Grant/Award Number:512301-I21502Hundred Talents Program of Zhejiang University,Grant/Award Number:188020*194231701/113。
文摘Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range.However,the limited absorption and serious backscattering of hot-electrons result in inadequate quantum yields,especially in the mid-infrared range.Here,we report a macroscopic assembled graphene(nMAG)nanofilm/silicon heterojunction for ultrafast mid-infrared photodetection.The assembled Schottky diode works in 1.5-4.0μm at room temperature with fast response(20-30 ns,rising time,4 mm2 window)and high detectivity(1.61011 to 1.9109 Jones from 1.5 to 4.0μm)under the pulsed laser,outperforming single-layer-graphene/silicon photodetectors by 2-8 orders.These performances are attributed to the greatly enhanced photo-thermionic effect of electrons in nMAG due to its high light absorption(~40%),long carrier relaxation time(~20 ps),low work function(4.52 eV),and suppressed carrier number fluctuation.The nMAG provides a long-range platform to understand the hot-carrier dynamics in bulk 2D materials,leading to broadband and ultrafast MIR active imaging devices at room temperature.
基金This work was supported by the Singapore Ministry of Education via AcRF Tier 3 Programme"Geometrical Quantum Materials"(MOE2018-T3-1-002)AcRF Tier 2 grants(MOE2017-T2-1-040,MOE2017-T2-1-001 and MOE2018-T2-02-068)+2 种基金Tier 1 grants(RG103/15 and RG113/16)Q.X.gratefully acknowledges the funding support from the National Natural Science Foundation of China(No.12020101003)a Tsinghua University start-up grant.
文摘Exciton-polariton condensation is regarded as a spontaneous macroscopic quantum phenomenon with phase ordering and collective coherence.By engineering artificial annular potential landscapes in halide perovskite semiconductor microcavities,we experimentally and theoretically demonstrate the room-temperature spontaneous formation of a coherent superposition of exciton-polariton orbital states with symmetric petal-shaped patterns in real space,resulting from symmetry breaking due to the anisotropic effective potential of the birefringent perovskite crystals.The lobe numbers of such petal-shaped polariton condensates can be precisely controlled by tuning the annular potential geometry.These petal-shaped condensates form in multiple orbital states,carrying locked alternating nphase shifts and vortex-anti vortex superposition cores,arising from the coupling of counterrotating exciton-polaritons in the confined circular waveguide.Our geometrically patterned microcavity exhibits promise for realizing room-temperature topological polaritonic devices and optical polaritonic switches based on periodic annular potentials.
基金Agency for Science,Technology and Research,Grant/Award Number:1527300025Central University Basic Research Fund of China,Grant/Award Numbers:020514380231,021014380177+5 种基金National Natural Science Foundation of China,Grant/Award Numbers:12104006,21873048,92056204National Research Foundation,Grant/Award Number:NRFNRFI2016-08Natural Science Foundation of Jiangsu Province,Grant/Award Number:BK20180319Start up fundations from Anhui UniversityTsinghua UniversityState Key Laboratory of Low-Dimensional Quantum Physics。
文摘Van der Waals heterojunctions are fast-emerging quantum structures fabricated by the controlled stacking of two-dimensional(2D)materials.Owing to the atomically thin thickness,their carrier properties are not only determined by the host material itself,but also defined by the interlayer interactions,including dielectric environment,charge trapping centers,and stacking angles.The abundant constituents without the limitation of lattice constant matching enable fascinating electrical,optical,and magnetic properties in van der Waals heterojunctions toward next-generation devices in photonics,optoelectronics,and information sciences.This review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides(TMDCs),a family of quantum materials with strong excitonic effects and unique valley properties,and other related 2D materials such as graphene and hexagonalboron nitride.In the first part,we summarize the ultrafast charge transfer processes in van der Waals heterojunctions,including its experimental evidence and theoretical understanding,the interlayer excitons at the TMDC interfaces,and the hot carrier injection at the graphene/TMDCs interface.In the second part,the energy transfer,including both Förster and Dexter types,are reviewed from both experimental and theoretical perspectives.Finally,we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field.
文摘We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.
基金Q.H.X.gratefully acknowledges the support from Singapore Ministry of Education via AcRF Tier 3 Programme(No.MOE2018-T3-1-002)Tier 2 project(No.MOE2017-T2-1-040)Singapore National Research Foundation via NRF-ANR project(No.NRF2017-NRF-ANR0052D-Chiral).
文摘Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications.Here,we investigated the carrier dynamics and many-body interactions in two-dimensional(2D)transition metal dichalcogenides(TMDs),using monolayer WS2 as an example,by employing femtosecond broadband pump-probe spectroscopy.Three time regimes for the exciton energy renormalization are unambiguously revealed with a distinct red-blue-red shift upon above-bandgap optical excitations.We attribute the dominant physical process in the three typical regimes to free carrier screening effect,Coulombic exciton-exciton interactions and Auger photocarrier generation,respectively,which show distinct dependence on the optical excitation wavelength,pump fluences and/or lattice temperature.An intrinsic exciton radiative lifetime of about 1.2 picoseconds(ps)in monolayer WS2 is unraveled at low temperature,and surprisingly the efficient Auger nonradiative decay of both bright and dark excitons puts the system in a nonequilibrium state at the nanosecond timescale.In addition,the dynamics of trions at low temperature is observed to be significantly different from that of excitons,e.g.,a long radiative lifetime of^108.7 ps at low excitation densities and the evolution of trion energy as a function of delay times.Our findings elucidate the dynamics of excitonic quasiparticles and the intricate many-body physics in 2D semiconductors,underpinning the future development of photonics,valleytronics and optoelectronics based on 2D semiconductors.
基金supported by the Natural Science Foundation of SZU (2017003)Shenzhen Science and Technology Research Grant (JCYJ20150324141711684)+2 种基金Singapore National Research Foundation (NRF-RF2009-06)an Investigator-ship Award (NRFNRFI2015-03)Ministry of Education (Singapore) via an AcRF Tier2 Grant (MOE2012-T2-2-086)
文摘The much slower progress in enhancing the thermoelectric performance of n-type Bi2Te3 than that of p-type Bi2Te3 based materials in the past decade hinders the widespread use in power generation and refrigeration. Here, a facile bottom-up solution-synthesis with spark plasma sintering(SPS) process has been developed to build n-type Bi2Te3-xSex bulk nanocomposites, which substantially improves the power factor and decreases the lattice thermal conductivity by tuning the interface scattering of phonons and electrons. The stoichiometric composition in ternary Bi2Te3-xSex nanocomposites is also tuned to optimize the carrier concentration and lattice thermal conductivity. The optimized bulk nanocomposite Bi2Te2.7Se0.3 exhibits a ZT of 1.1 at^371 K, which is comparable to the corresponding commercially available ingots. Our results demonstrate the great potential of the solution-processed n-type Bi2Te3-xSex nanocomposites for cost-effective thermoelectric applications.
文摘The exciting progress in graphene research in the past 15 years[1,2] has further stimulated the exploration of other non-graphene two-dimensional (2D) materials [3], such as h-BN [4,5], transitional metal dichalcogenides (TMDs)[6,7], black phosphorene [8],etc. Research on these ultimately atomic thin 2D materials has grown exponentially owning to their fascinating properties and enormous potential in the fields of physics, chemistry, optics and photonics, material sciences, medicine and engineering.
基金support from Singapore Ministry of Education via Ac RF Tier3 Programme“Geometrical Quantum Materials”(MOE2018-T3-1-002),Ac RF Tier2 grant(MOE2017-T2-1-040)and Tier1 grant(RG 194/17)funding from the National Research Foundation,Prime Ministers Office,Singapore,under its Medium-Sized Centre Programmethe funding from MOE2017-T2-2-139。
文摘Introducing magnetic dopants into twodimensional transition metal dichalcogenides has recently attracted considerable attention due to its promising applications in spintronics and valleytronics.Herein we realized manganese-doped molybdenum diselenide(MoSe_(2))single crystal via chemical vapor transport(CVT)reaction,containing up to 2.9%(atomic concentration)Mn dopants,and investigated the light-matter interaction in these samples.We observed a suppressed trion intensity,a longer photoluminescence lifetime,and prominent blue-and red-shift of E_(2g)^(2)(in-plane)and A_(1g)(out-of-plane)Raman modes,respectively.Moreover,the Mn dopants increase the valley Zeeman splitting of the MoSe_(2) monolayer by~50%,while preserving the linear dependence on magnetic field.First-principles calculations indicate that the spin-polarized deep level defect states are formed due to the Mn substitutional dopants in the Mo Se_(2) lattice.The resulting defect potential favors the funnelling of excitons towards the defects.The Mn dopants reduce the magnitude of the interatomic force constants,explaining the red-shift of the A_(1g)mode.The Mn atoms and their immediate Mo and Se neighbors carry significant magnetic moments,which enhance the observed exciton g-factors due to the exchange interactions affecting defect-bound excitons.
基金National Natural Science Foundation of China(grant No.12020101003,and 12250710126)funding support from the State Key Laboratory of Low-Dimensional Quantum Physics of Tsinghua University and the Tsinghua University Initiative Scientific Research Program.
文摘Exciton polaritons in atomically thin transition-metal dichalcogenide microcavities provide a versatile platform for advancing optoelectronic devices and studying the interacting Bosonic physics at ambient conditions.Rationally engineering the favorable properties of polaritons is critically required for the rapidly growing research.Here,we demonstrate the manipulation of nonlinear polaritons with the lithographically defined potential landscapes in monolayer WS_(2)microcavities.The discretization of photoluminescence dispersions and spatially confined patterns indicate the deterministic on-site localization of polaritons by the artificial mesa cavities.Varying the trapping sizes,the polariton-reservoir interaction strength is enhanced by about six times through managing the polariton–exciton spatial overlap.Meanwhile,the coherence of trapped polaritons is significantly improved due to the spectral narrowing and tailored in a picosecond range.Therefore,our work not only offers a convenient approach to manipulating the nonlinearity and coherence of polaritons but also opens up possibilities for exploring many-body phenomena and developing novel polaritonic devices based on 2D materials.
文摘Halide perovskite semiconductors have emerged as promising candidates for the next-generation low-energy consumption,high-flexibility photonics and optoelectronic devices thanks to their superior optical and excitonic properties as well as fabrication convenience.This special issue,including three review papers and six original research papers,focuses on the studies of both fundamentals and applications of perovskite photonics,covering materials,excitonic properties,nonlinear optics,strong light–matter interactions,and optoelectronic devices.
文摘The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.
