We investigated the one-dimensional diamond ladder in the momentum lattice platform. By inducing multiple twoand four-photon Bragg scatterings among specific momentum states, we achieved a flat band system based on th...We investigated the one-dimensional diamond ladder in the momentum lattice platform. By inducing multiple twoand four-photon Bragg scatterings among specific momentum states, we achieved a flat band system based on the diamond model, precisely controlling the coupling strength and phase between individual lattice sites. Utilizing two lattice sites couplings, we generated a compact localized state associated with the flat band, which remained localized throughout the entire time evolution. We successfully realized the continuous shift of flat bands by adjusting the corresponding nearest neighbor hopping strength, enabling us to observe the complete localization process. This opens avenues for further exploration of more complex properties within flat-band systems, including investigating the robustness of flat-band localized states in disordered flat-band systems and exploring many-body localization in interacting flat-band systems.展开更多
Electronic circular dichroism(ECD)spectrum is an important tool for as-sessing molecular chirality.Tradition-al methods,like linear response time-dependent density functional theory(LR-TDDFT),predict ECD spectra well ...Electronic circular dichroism(ECD)spectrum is an important tool for as-sessing molecular chirality.Tradition-al methods,like linear response time-dependent density functional theory(LR-TDDFT),predict ECD spectra well for small or medium-sized molecules,but struggle with large sys-tems due to high computational costs,making it a significant challenge to ac-curately and efficiently predict the ECD properties of complex systems.Within the framework of the generalized energy-based fragmentation(GEBF)method for localized excited states(ESs)calculation,we propose a combination algorithm for calculating rotatory strengths of ESs in condensed phase systems.This algorithm estimates the rotatory strength of the total system by calculating and combin-ing the transition electric and magnetic dipole moments of subsystems.We have used the GEBF method to calculate the ECD properties of chiral drug molecule derivatives,green fluo-rescent protein,and cyclodextrin derivatives,and compared their results with traditional methods or experimental data.The results show that this method can efficiently and accu-rately predict the ECD spectra of these systems.Thus,the GEBF method for ECD spectra demonstrates great potential in the chiral analysis of complex systems and chiral material design,promising to become a powerful theoretical tool in chiral chemistry.展开更多
A pair of asymmetric rigid carbazole-benzonitrile-based emitters were synthesized by strategically alternating donor and acceptor groups along the molecular edges.The spin-flip process is accelerated by both the forma...A pair of asymmetric rigid carbazole-benzonitrile-based emitters were synthesized by strategically alternating donor and acceptor groups along the molecular edges.The spin-flip process is accelerated by both the formation of localized and delocalized charge transfer states due to linearly positioned donors and strong spin-orbital coupling between different excitation feature of the lowest singlet and triplet excited states.This molecular architecture results in a remarkable short delayed lifespan of around 100 ns.The application of the two emitters in organic light-emitting diodes(OLEDs)achieves the highest external quantum efficiencies of 13.0%for the green emitter and 9.1%for the sky-blue emitter.Impressively,these devices maintain their high efficiency even at high luminance levels.The sustained efficiency is ascribed to the effective suppression of exciton quenching by substantially shortening delayed lifespan.These findings underscore the practical utility of the molecular design strategy that incorporates alternate donor and acceptor groups at the molecular periphery for shortening delayed fluorescence lifetime,and hold great promise for the development of high-performance OLEDs.展开更多
Lattice distortion of materials has a profound impact on their electronic and magnetic properties,which can generate local magnetic states in intrinsically non-magnetic systems.Here we report on the realization of a o...Lattice distortion of materials has a profound impact on their electronic and magnetic properties,which can generate local magnetic states in intrinsically non-magnetic systems.Here we report on the realization of a one-dimensional(1D)magnetic stripe in monolayer H-NbSe_(2)sustained by strain along the terraces of the graphene/SiC substrates.The strength of this tensile strain is widely tunable by the height-to-width ratio of the terraces.Increasing the tensile strength leads to the shifts and splitting of the Nb 4d bands crossing the Fermi energy,generating spin polarization in a 1D magnetic stripe along the terrace.Simultaneously,the charge-densitywave signature of strained H-NbSe_(2)is significantly suppressed.Such a magnetic stripe can be locally quenched by an individual Se-atom defect via the defect-induced Jahn-Teller distortion and charge density redistribution.These findings provide a different route to achieving and manipulating 1D magnetism in otherwise non-magnetic systems,offering a new way for spintronic devices.展开更多
We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of ...We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of the rolls perpendic- ular to their axes. For a negative enough separation ratio, two types of quite different confined states were documented by applying different control processes. One branch of localized travelling waves survives only in a very narrow band within subcritical regime, while another branch straddles the onset of convection existing both in subcritical and super- critical regions. We elucidated that concentration field and its current are key to understand how confined convection is sustained when conductive state is absolutely unstable, The weak structures in the conducting region are demonstrated too.展开更多
Dirac particle penetration is studied theoretically with Dirac equation in one-dimensional systems. We investigate a one-dimensional system with N barriers where both barrier height and well width are constants random...Dirac particle penetration is studied theoretically with Dirac equation in one-dimensional systems. We investigate a one-dimensional system with N barriers where both barrier height and well width are constants randomly distributed in certain range. The one-parameter scaling theory for nonrelatiyistic particles is still valid for massive Dirac particles. In the same disorder sample, we find that the localization length of relativistic particles is always larger than that of nonrelativistic particles and the transmission coefficient related to incident particle in both cases fits the form T～ exp（-αL）. More interesting, massless relativistic particles are entirely delocalized no matter how big the energy of incident particles is.展开更多
Routing algorithms in satellite constellation networks usually make use of the local state information to adapt to the topology and traffic dynamics,since it’s difficult to obtain the global states in time due to the...Routing algorithms in satellite constellation networks usually make use of the local state information to adapt to the topology and traffic dynamics,since it’s difficult to obtain the global states in time due to the spatial large-scale feature of constellation networks.Furthermore,they use different range of local states and give these states distinct weights.However,the behind design criterion is ambiguous and often based on experience.This paper discusses the problem from the perspective of complex network.A universal local-state routing model with tunable parameters is presented to generalize the common characteristics of local-state routing algorithms for satellite constellation networks.Based on this,the impacts of localstate routing algorithms on performance and the correlation between routing and traffic dynamics are analyzed in detail.Among them,the tunable parameters,the congestion propagation process,the critical packet sending rate,and the network robustness are discussed respectively.Experimental results show that routing algorithms can achieve a satisfactory performance by maintaining a limited state awareness capability and obtaining the states in a range below the average path length.This provides a valuable design basis for routing algorithms in satellite constellation networks.展开更多
A new nanolaser concept using silicon quantum dots （QDs） is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on S...A new nanolaser concept using silicon quantum dots （QDs） is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on Si QDs can be formed for the activation of emission. An inversion of population can be generated between the localized states and the valence band in a QD fabricated by using a nanosecond pulse laser. Coupling between the active centres formed by localized states and the defect states of the two-dimensional （2D） photonic crystal can be used to select the model in the nanolaser.展开更多
We consider a three-electron system in the Impurity Hubbard model with a coupling between nearest-neighbors. Our research aim consists of studying the structure of essential spectrum and discrete spectra of the energy...We consider a three-electron system in the Impurity Hubbard model with a coupling between nearest-neighbors. Our research aim consists of studying the structure of essential spectrum and discrete spectra of the energy operator of three-electron systems in the impurity Hubbard model in the quartet state of the system in a <em>v</em>-dimensional lattice. We have reduced the study of the spectrum of the three-electron quartet state operator in the impurity Hubbard model to the study of the spectrum of a simpler operator. We proved the essential spectra of the three-electron systems in the Impurity Hubbard model in the quartet state is the union of no more than six segments, and the discrete spectrum of the system is consists of no more than four eigenvalues.展开更多
The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states...The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states.The large-scale calculation of vortex bound states is introduced in the presence of fourfold or twofold Fermi surface by solving the Bogoliubov–de Gennes(BdG)equations.Two kinds of quasiparticles’behaviors can be extracted from the local density of states(LDOS)around a vortex.The angle-dependent quasiparticles will move from high energy to low energy when the angle varies from curvature maxima to minima of the Fermi surface,while the angle-independent quasiparticles tend to stay at a relatively higher energy.In addition,the weight of angle-dependent quasiparticles can be enhanced by the increasing anisotropy degree of Fermi surface.展开更多
The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion ...The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit “mountain chain” structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electricdisplacement vector at the interface. In the frequency range of the pseudo-PBG （photonic band gap）, the LDPS keeps very low value over the whole Wiger-Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.展开更多
In this paper we propose a type of new analytical method to investigate the localized states in the armchair graphene-like nanoribbons. The method is based on the tight-binding model and with a standing wave assumptio...In this paper we propose a type of new analytical method to investigate the localized states in the armchair graphene-like nanoribbons. The method is based on the tight-binding model and with a standing wave assumption. The system of armchair graphene-like nanoribbons includes the armchair supercells with arbitrary elongation-type line defects and the semi-infinite nanoribbons. With this method, we analyze many interesting localized states near the line defects in the graphene and boron-nitride nanoribbons. We also derive the analytical expressions and the criteria for the localized states in the semi-infinite nanoribbons.展开更多
A flattened elliptic ring containing an electron is studied. The emphasis is placed on clarifying the effect of the flattening. The localized states are classified into four types according to their inherent nodes. Wh...A flattened elliptic ring containing an electron is studied. The emphasis is placed on clarifying the effect of the flattening. The localized states are classified into four types according to their inherent nodes. When the ring becomes more flattened, the total probability of dipole absorption of each state is found to be reduced. Furthermore, each spectral line of absorption is found to shift towards red and may split into a few lines, and these lines as a whole become more diffusive.展开更多
Hole-net structure silicon is fabricated by laser irradiation and annealing, on which a photoluminescence （PL） band in a the region of 650-750 nm is pinned and its intensity increases obviously after oxidation. It i...Hole-net structure silicon is fabricated by laser irradiation and annealing, on which a photoluminescence （PL） band in a the region of 650-750 nm is pinned and its intensity increases obviously after oxidation. It is found that the PL intensity changes with both laser irradiation time and annealing time. Calculations show that some localized states appear in the band gap of the smaller nanocrystal when Silo bonds or Si-O-Si bonds are passivated on the surface. It is discovered that the density and the number of Si=O bonds or Si-O-Si bonds related to both the irradiation time and the annealing time obviously affect the generation of the localized gap states of hole-net silicon, by which the production of stimulated emission through controlling oxidation time can be explained.展开更多
We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite...We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.展开更多
The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point of...The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point off the centre （for example, at the point （0.3a, 0.4a）, where a is the lattice constant） is extremely enhanced. Further, the disordered radii are introduced to imitate the real devices fabricated in our experiment, and then we study the LDOS of PhC cavity with configurations of different disordered radii. The results show that in the disordered cavity, the LDOS in the centre is still greatly reduced, while the LDOS at the point （0.3a, 0.4a） is still extremely enhanced. It shows that the LDOS analysis is useful. When a laser is designed on the basis of the square lattice PhC rod cavity, in order to enhance the spontaneous emission, the active materials should not be inserted in the centre of the cavity, but located at positions off the centre. So LDOS method gives a guide to design the positions of the active materials （quantum dots） in the lasers.展开更多
The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and ...The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and the LDOS is established.Then,based on the transfer matrix method and the effective resonator model,the leaky loss of the leaky mode and the mode spectrum in the one-dimensional photonic bandgap crystal waveguide are calculated,results of which indicate that the mode spectrum can characterize the leaky loss of the leaky mode.At last,the density of optical states(DOS),and the LDOS in each layer are calculated.The partial DOS and the partial LDOS in the quantum well,related to the fundamental leaky mode,can be used to find out the optimal location of the quantum well in the defect layer to couple more useful photons into the lasing mode for lasers.展开更多
The single-particle Green＇s function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U（t,t＇） method and Floquet-Green＇s function. ...The single-particle Green＇s function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U（t,t＇） method and Floquet-Green＇s function. The calculation of the local density of states shows that new states will emerge between the resonant Wannier-Stark states as a result of the intervention of time-dependent impurity potential, and the increase in electric field strength of impurity will result in the growing of the number of new states between the gaps of neighbouring Stark ladders.展开更多
The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased...The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased of Zn concentration in the glassy alloys. The activation energy (ΔE) decreases with increase of Zn content. The conduction is explained on the basis of localized state in the mobility gap. To study the effect of electric field, a Current-Voltage characteristic has been measured at various fixed temperatures. The Current-Voltage data are fitted into the theory of space charge limited conduction in case of uniform distribution of traps in mobility gap at high electric fields (E ~104 V/cm) of these materials. The density of localized state (g0) are estimated by fitting in theory of space charge limited conduction (SCLC) at the temperature range of (352 - 372 K) in the glassy Se100–xZnx. The density of localized state (0) near the Fermi level are increases with increase of Zn concentration in the (Se100–xZnx) thin films and explain on the basis of increase of the Zn-Se bond.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.12074367)Anhui Initiative in Quantum Information Technologies,the National Key Research and Development Program of China (Grant No.2020YFA0309804)+3 种基金Shanghai Municipal Science and Technology Major Project (Grant No.2019SHZDZX01)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDB35020200)Innovation Program for Quantum Science and Technology (Grant No.2021ZD0302002)New Cornerstone Science Foundation。
文摘We investigated the one-dimensional diamond ladder in the momentum lattice platform. By inducing multiple twoand four-photon Bragg scatterings among specific momentum states, we achieved a flat band system based on the diamond model, precisely controlling the coupling strength and phase between individual lattice sites. Utilizing two lattice sites couplings, we generated a compact localized state associated with the flat band, which remained localized throughout the entire time evolution. We successfully realized the continuous shift of flat bands by adjusting the corresponding nearest neighbor hopping strength, enabling us to observe the complete localization process. This opens avenues for further exploration of more complex properties within flat-band systems, including investigating the robustness of flat-band localized states in disordered flat-band systems and exploring many-body localization in interacting flat-band systems.
基金supported by the National Natural Science Foundation of China(No.22273038 and No.22033004).
文摘Electronic circular dichroism(ECD)spectrum is an important tool for as-sessing molecular chirality.Tradition-al methods,like linear response time-dependent density functional theory(LR-TDDFT),predict ECD spectra well for small or medium-sized molecules,but struggle with large sys-tems due to high computational costs,making it a significant challenge to ac-curately and efficiently predict the ECD properties of complex systems.Within the framework of the generalized energy-based fragmentation(GEBF)method for localized excited states(ESs)calculation,we propose a combination algorithm for calculating rotatory strengths of ESs in condensed phase systems.This algorithm estimates the rotatory strength of the total system by calculating and combin-ing the transition electric and magnetic dipole moments of subsystems.We have used the GEBF method to calculate the ECD properties of chiral drug molecule derivatives,green fluo-rescent protein,and cyclodextrin derivatives,and compared their results with traditional methods or experimental data.The results show that this method can efficiently and accu-rately predict the ECD spectra of these systems.Thus,the GEBF method for ECD spectra demonstrates great potential in the chiral analysis of complex systems and chiral material design,promising to become a powerful theoretical tool in chiral chemistry.
基金supported by the National Natural Science Foundation of China(Nos.T2441002 and 22175186)。
文摘A pair of asymmetric rigid carbazole-benzonitrile-based emitters were synthesized by strategically alternating donor and acceptor groups along the molecular edges.The spin-flip process is accelerated by both the formation of localized and delocalized charge transfer states due to linearly positioned donors and strong spin-orbital coupling between different excitation feature of the lowest singlet and triplet excited states.This molecular architecture results in a remarkable short delayed lifespan of around 100 ns.The application of the two emitters in organic light-emitting diodes(OLEDs)achieves the highest external quantum efficiencies of 13.0%for the green emitter and 9.1%for the sky-blue emitter.Impressively,these devices maintain their high efficiency even at high luminance levels.The sustained efficiency is ascribed to the effective suppression of exciton quenching by substantially shortening delayed lifespan.These findings underscore the practical utility of the molecular design strategy that incorporates alternate donor and acceptor groups at the molecular periphery for shortening delayed fluorescence lifetime,and hold great promise for the development of high-performance OLEDs.
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1402602,2022YFA1402502,2021YFA1400103,2020YFA0308802,and 2024YFA1611300)the National Natural Science Foundation of China(Grant Nos.92163206,12274026,12321004,12304205,11934003,12393831,and U2230402)+1 种基金Beijing Association for Science and Technology Youth Talent Lift Program,MCIN/AEI/10.13039/501100011033(Grant No.PID2022-140845OB-C66)FEDER Una manera de hacer Europa。
文摘Lattice distortion of materials has a profound impact on their electronic and magnetic properties,which can generate local magnetic states in intrinsically non-magnetic systems.Here we report on the realization of a one-dimensional(1D)magnetic stripe in monolayer H-NbSe_(2)sustained by strain along the terraces of the graphene/SiC substrates.The strength of this tensile strain is widely tunable by the height-to-width ratio of the terraces.Increasing the tensile strength leads to the shifts and splitting of the Nb 4d bands crossing the Fermi energy,generating spin polarization in a 1D magnetic stripe along the terrace.Simultaneously,the charge-densitywave signature of strained H-NbSe_(2)is significantly suppressed.Such a magnetic stripe can be locally quenched by an individual Se-atom defect via the defect-induced Jahn-Teller distortion and charge density redistribution.These findings provide a different route to achieving and manipulating 1D magnetism in otherwise non-magnetic systems,offering a new way for spintronic devices.
文摘We have performed numerical simulations of localized travelling-wave convection in a binary fluid mixture heated from below in a long rectangular container. Calculations are carried out in a vertical cross section of the rolls perpendic- ular to their axes. For a negative enough separation ratio, two types of quite different confined states were documented by applying different control processes. One branch of localized travelling waves survives only in a very narrow band within subcritical regime, while another branch straddles the onset of convection existing both in subcritical and super- critical regions. We elucidated that concentration field and its current are key to understand how confined convection is sustained when conductive state is absolutely unstable, The weak structures in the conducting region are demonstrated too.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 10174024 and 10474025
文摘Dirac particle penetration is studied theoretically with Dirac equation in one-dimensional systems. We investigate a one-dimensional system with N barriers where both barrier height and well width are constants randomly distributed in certain range. The one-parameter scaling theory for nonrelatiyistic particles is still valid for massive Dirac particles. In the same disorder sample, we find that the localization length of relativistic particles is always larger than that of nonrelativistic particles and the transmission coefficient related to incident particle in both cases fits the form T～ exp（-αL）. More interesting, massless relativistic particles are entirely delocalized no matter how big the energy of incident particles is.
基金supported in part by the National Natural Science Foundation of China under Grant 62171466and the National Natural Science Foundation of China under Grant 61971440+1 种基金the National Key R&D Program of China under Grant 2018YFB1801103the Natural Science Foundation on Frontier Leading Technology Basic Research Project of Jiangsu under Grant BK20192002。
文摘Routing algorithms in satellite constellation networks usually make use of the local state information to adapt to the topology and traffic dynamics,since it’s difficult to obtain the global states in time due to the spatial large-scale feature of constellation networks.Furthermore,they use different range of local states and give these states distinct weights.However,the behind design criterion is ambiguous and often based on experience.This paper discusses the problem from the perspective of complex network.A universal local-state routing model with tunable parameters is presented to generalize the common characteristics of local-state routing algorithms for satellite constellation networks.Based on this,the impacts of localstate routing algorithms on performance and the correlation between routing and traffic dynamics are analyzed in detail.Among them,the tunable parameters,the congestion propagation process,the critical packet sending rate,and the network robustness are discussed respectively.Experimental results show that routing algorithms can achieve a satisfactory performance by maintaining a limited state awareness capability and obtaining the states in a range below the average path length.This provides a valuable design basis for routing algorithms in satellite constellation networks.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60966002)the National Key Laboratory Fund of Surface Physics at Fudan University,(Grant No. 20090606)
文摘A new nanolaser concept using silicon quantum dots （QDs） is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on Si QDs can be formed for the activation of emission. An inversion of population can be generated between the localized states and the valence band in a QD fabricated by using a nanosecond pulse laser. Coupling between the active centres formed by localized states and the defect states of the two-dimensional （2D） photonic crystal can be used to select the model in the nanolaser.
文摘We consider a three-electron system in the Impurity Hubbard model with a coupling between nearest-neighbors. Our research aim consists of studying the structure of essential spectrum and discrete spectra of the energy operator of three-electron systems in the impurity Hubbard model in the quartet state of the system in a <em>v</em>-dimensional lattice. We have reduced the study of the spectrum of the three-electron quartet state operator in the impurity Hubbard model to the study of the spectrum of a simpler operator. We proved the essential spectra of the three-electron systems in the Impurity Hubbard model in the quartet state is the union of no more than six segments, and the discrete spectrum of the system is consists of no more than four eigenvalues.
基金the National Natural Science Foundation of China(Grant No.11804154)Scientific Research Foundation of NJIT(Grant No.YKJ201853).
文摘The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states.The large-scale calculation of vortex bound states is introduced in the presence of fourfold or twofold Fermi surface by solving the Bogoliubov–de Gennes(BdG)equations.Two kinds of quasiparticles’behaviors can be extracted from the local density of states(LDOS)around a vortex.The angle-dependent quasiparticles will move from high energy to low energy when the angle varies from curvature maxima to minima of the Fermi surface,while the angle-independent quasiparticles tend to stay at a relatively higher energy.In addition,the weight of angle-dependent quasiparticles can be enhanced by the increasing anisotropy degree of Fermi surface.
基金Project supported by National Key Basic Research Special Fund of China and by Natural Science Foundation of Beijing, China.
文摘The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit “mountain chain” structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electricdisplacement vector at the interface. In the frequency range of the pseudo-PBG （photonic band gap）, the LDPS keeps very low value over the whole Wiger-Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.
基金Project supported by the Starting Foundation for the‘Hundred Talent Program’of Chongqing University,China(Grants No.0233001104429)
文摘In this paper we propose a type of new analytical method to investigate the localized states in the armchair graphene-like nanoribbons. The method is based on the tight-binding model and with a standing wave assumption. The system of armchair graphene-like nanoribbons includes the armchair supercells with arbitrary elongation-type line defects and the semi-infinite nanoribbons. With this method, we analyze many interesting localized states near the line defects in the graphene and boron-nitride nanoribbons. We also derive the analytical expressions and the criteria for the localized states in the semi-infinite nanoribbons.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10574163 and 10675174)
文摘A flattened elliptic ring containing an electron is studied. The emphasis is placed on clarifying the effect of the flattening. The localized states are classified into four types according to their inherent nodes. When the ring becomes more flattened, the total probability of dipole absorption of each state is found to be reduced. Furthermore, each spectral line of absorption is found to shift towards red and may split into a few lines, and these lines as a whole become more diffusive.
基金Project supported by the National Natural Science Foundation of China (Grant No 10764002)
文摘Hole-net structure silicon is fabricated by laser irradiation and annealing, on which a photoluminescence （PL） band in a the region of 650-750 nm is pinned and its intensity increases obviously after oxidation. It is found that the PL intensity changes with both laser irradiation time and annealing time. Calculations show that some localized states appear in the band gap of the smaller nanocrystal when Silo bonds or Si-O-Si bonds are passivated on the surface. It is discovered that the density and the number of Si=O bonds or Si-O-Si bonds related to both the irradiation time and the annealing time obviously affect the generation of the localized gap states of hole-net silicon, by which the production of stimulated emission through controlling oxidation time can be explained.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274108)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20114306110008)the Hunan Provincial Innovation Foundation for Postgraduates(Grant No.CX2012B204)
文摘We study the local density of states （LDOS） for electrons scattering off the line edge of an atomic step defect on the surface of a three-dimensional （3D） topological insulator （TI） and the line edge of a finite 3D TI, where the front surface and side surface meet with different Fermi velocities, respectively. By using a S-function potential to model the edges, we find that the bound states existed along the step line edge significantly contribute to the LDOS near the edge, but do not modify the exponential behavior away from it. In addition, the power-law decaying behavior for LDOS oscillation away from the step is understood from the spin rotation for surface states scattering off the step defect with magnitude depending on the strength of the potential. Furthermore, the electron refraction and total reflection analogous to optics occurred at the line edge where two surfaces meet with different Fermi velocities, which leads to the LDOS decaying behavior in the greater Fermi velocity side similar to that for a step line edge. However, in the smaller velocity side the LDOS shows a different decaying behavior as x-1/2, and the wavevector of LDOS oscillation is no longer equal to the diameter of the constant energy contour of surface band, but is sensitively dependent on the ratio of the two Fermi velocities. These effects may be verified by STM measurement with high precision.
基金supported by the National Basic Research Program of China (Grant No. 2006CB921705)the National Natural Science Foundation of China (Grant Nos. 10634080,60677046 and 60838003)the National High Technology Research and Development Program of China (Grant Nos. 2007AA03Z410 and 2007AA03Z408)
文摘The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point off the centre （for example, at the point （0.3a, 0.4a）, where a is the lattice constant） is extremely enhanced. Further, the disordered radii are introduced to imitate the real devices fabricated in our experiment, and then we study the LDOS of PhC cavity with configurations of different disordered radii. The results show that in the disordered cavity, the LDOS in the centre is still greatly reduced, while the LDOS at the point （0.3a, 0.4a） is still extremely enhanced. It shows that the LDOS analysis is useful. When a laser is designed on the basis of the square lattice PhC rod cavity, in order to enhance the spontaneous emission, the active materials should not be inserted in the centre of the cavity, but located at positions off the centre. So LDOS method gives a guide to design the positions of the active materials （quantum dots） in the lasers.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2021YFA1400604 and 2021YFB2801400)the National Natural Science Foundation of China(Grant Nos.91850206,62075213,62135001,and 62205328)。
文摘The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and the LDOS is established.Then,based on the transfer matrix method and the effective resonator model,the leaky loss of the leaky mode and the mode spectrum in the one-dimensional photonic bandgap crystal waveguide are calculated,results of which indicate that the mode spectrum can characterize the leaky loss of the leaky mode.At last,the density of optical states(DOS),and the LDOS in each layer are calculated.The partial DOS and the partial LDOS in the quantum well,related to the fundamental leaky mode,can be used to find out the optimal location of the quantum well in the defect layer to couple more useful photons into the lasing mode for lasers.
基金Project supported by the Natural Science Foundation of Shanxi Province （Grant No 20031006）.
文摘The single-particle Green＇s function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U（t,t＇） method and Floquet-Green＇s function. The calculation of the local density of states shows that new states will emerge between the resonant Wannier-Stark states as a result of the intervention of time-dependent impurity potential, and the increase in electric field strength of impurity will result in the growing of the number of new states between the gaps of neighbouring Stark ladders.
文摘The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased of Zn concentration in the glassy alloys. The activation energy (ΔE) decreases with increase of Zn content. The conduction is explained on the basis of localized state in the mobility gap. To study the effect of electric field, a Current-Voltage characteristic has been measured at various fixed temperatures. The Current-Voltage data are fitted into the theory of space charge limited conduction in case of uniform distribution of traps in mobility gap at high electric fields (E ~104 V/cm) of these materials. The density of localized state (g0) are estimated by fitting in theory of space charge limited conduction (SCLC) at the temperature range of (352 - 372 K) in the glassy Se100–xZnx. The density of localized state (0) near the Fermi level are increases with increase of Zn concentration in the (Se100–xZnx) thin films and explain on the basis of increase of the Zn-Se bond.
