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
Monolayer phosphorene provides a unique two-dimensional(2D)platform to investigate the fundamental dynamics of excitons and trions(charged excitons)in reduced dimensions.However,owing to its high instability,unambiguo...Monolayer phosphorene provides a unique two-dimensional(2D)platform to investigate the fundamental dynamics of excitons and trions(charged excitons)in reduced dimensions.However,owing to its high instability,unambiguous identification of monolayer phosphorene has been elusive.Consequently,many important fundamental properties,such as exciton dynamics,remain underexplored.We report a rapid,noninvasive,and highly accurate approach based on optical interferometry to determine the layer number of phosphorene,and confirm the results with reliable photoluminescence measurements.Furthermore,we successfully probed the dynamics of excitons and trions in monolayer phosphorene by controlling the photo-carrier injection in a relatively low excitation power range.Based on our measured optical gap and the previously measured electronic energy gap,we determined the exciton binding energy to be~0.3 eV for the monolayer phosphorene on SiO_(2)/Si substrate,which agrees well with theoretical predictions.A huge trion binding energy of~100 meV was first observed in monolayer phosphorene,which is around five times higher than that in transition metal dichalcogenide(TMD)monolayer semiconductor,such as MoS_(2).The carrier lifetime of exciton emission in monolayer phosphorene was measured to be,220 ps,which is comparable to those in other 2D TMD semiconductors.Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene.展开更多
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.
基金financial support from the ANU PhD scholarship,the China Research Council PhD scholarship,the National Science Foundation(USA,grant number ECCS-1405201)the Australian Research Council(grant number DE140100805),and the ANU Major Equipment Committee.
文摘Monolayer phosphorene provides a unique two-dimensional(2D)platform to investigate the fundamental dynamics of excitons and trions(charged excitons)in reduced dimensions.However,owing to its high instability,unambiguous identification of monolayer phosphorene has been elusive.Consequently,many important fundamental properties,such as exciton dynamics,remain underexplored.We report a rapid,noninvasive,and highly accurate approach based on optical interferometry to determine the layer number of phosphorene,and confirm the results with reliable photoluminescence measurements.Furthermore,we successfully probed the dynamics of excitons and trions in monolayer phosphorene by controlling the photo-carrier injection in a relatively low excitation power range.Based on our measured optical gap and the previously measured electronic energy gap,we determined the exciton binding energy to be~0.3 eV for the monolayer phosphorene on SiO_(2)/Si substrate,which agrees well with theoretical predictions.A huge trion binding energy of~100 meV was first observed in monolayer phosphorene,which is around five times higher than that in transition metal dichalcogenide(TMD)monolayer semiconductor,such as MoS_(2).The carrier lifetime of exciton emission in monolayer phosphorene was measured to be,220 ps,which is comparable to those in other 2D TMD semiconductors.Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene.