Based on the Gross–Pitaevskii equation,we theoretically investigate exciton Bose–Einstein condensation(BEC)in transition metal dichalcogenide monolayers(TMDC-MLs)under in-plane magnetic fields.We observe that the in...Based on the Gross–Pitaevskii equation,we theoretically investigate exciton Bose–Einstein condensation(BEC)in transition metal dichalcogenide monolayers(TMDC-MLs)under in-plane magnetic fields.We observe that the in-plane magnetic fields exert a strong influence on the exciton BEC wave functions in TMDC-MLs because of the mixing of the bright and dark exciton states via Zeeman effect.This leads to the brightening of the dark exciton BEC states.The competition between the dipole–dipole interactions caused by the long-range Coulomb interaction and the Zeeman effect induced by the in-plane magnetic fields can effectively regulate dark exciton BEC states.Our findings emphasize the utility of TMD-MLs as platforms for investigating collective phenomenon involving excited states.展开更多
Quasi-one-dimensional(1D)graphene nanoribbons(GNRs)play a crucial role in advancement of nextgeneration devices.Recent studies have suggested their potential to exhibit unique symmetry-protected topological phases def...Quasi-one-dimensional(1D)graphene nanoribbons(GNRs)play a crucial role in advancement of nextgeneration devices.Recent studies have suggested their potential to exhibit unique symmetry-protected topological phases defined by a Z_(2) invariant.By employing both the tight-binding model and the Floquet theory,our investigation demonstrates the effective control of the topological phase within quasi-1D armchair GNRs(AGNRs)using elliptically polarized light,unveiling rich topological phase diagrams.Specifically,we observe that varying the amplitude of the light can induce transitions in the band gap(E_(g))of AGNRs,leading to multiple changes in the system’s Z_(2) invariant.Furthermore,for heterojunctions composed of different AGNR segments,the junction state can be either created or eliminated by the application of elliptically polarized light.展开更多
The evolution process of magnetic domains in response to external fields is crucial for the modern understanding and application of spintronics.In this study,we investigated the domain rotation in stripe domain films ...The evolution process of magnetic domains in response to external fields is crucial for the modern understanding and application of spintronics.In this study,we investigated the domain rotation in stripe domain films of varying thicknesses by examining their response to microwave excitation in four different orientations.The resonance spectra indicate that the rotation field of stripe domain film under an applied magnetic field approaches the field where the resonance mode of sample changes.The saturation field of the stripe domain film corresponds to the field where the resonance mode disappears when measured in the stripe direction parallel to the microwave magnetic field.The results are reproducible and consistent with micromagnetic simulations,providing additional approaches and techniques for comprehending the microscopic mechanisms of magnetic domains and characterizing their rotation.展开更多
Janus WSSe monolayer is a novel two-dimensional(2D)material that breaks the out-of-plane mirror symmetry and has a large built-in electric field.These features lead to sizable Rashba spin-orbit coupling and enhanced n...Janus WSSe monolayer is a novel two-dimensional(2D)material that breaks the out-of-plane mirror symmetry and has a large built-in electric field.These features lead to sizable Rashba spin-orbit coupling and enhanced nonlinear optical properties,making it a promising material platform for various spintronic and optoelectronic device applications.In recent years,nonlinear photocurrent responses such as shift and injection currents were found to be closely related to the quantum geometry and Berry curvature of materials,indicating that these responses can serve as powerful tools for probing the novel quantum properties of materials.In this work,we investigate the second-order nonlinear photocurrent responses in a Janus WSSe monolayer theoretically based on first-principles calculations and the Wannier interpolation method.It is demonstrated that the Janus WSSe monolayer exhibits significant out-of-plane nonlinear photocurrent coefficients,which is distinct from the nonJanus structures.Our results also suggest that the second-order nonlinear photocurrent response in the Janus WSSe monolayer can be effectively tuned by biaxial strain or an external electric field.Thus,the Janus WSSe monolayer offers a unique opportunity for both exploring nonlinear optical phenomena and realizing flexible 2D optoelectronic nanodevices.展开更多
We study electronic spin-polarised transport in a system composed of a quantum dot(QD)connected to one normal metal electrode and one ferromagnetic one.The electrical current of each spin component and the spin accumu...We study electronic spin-polarised transport in a system composed of a quantum dot(QD)connected to one normal metal electrode and one ferromagnetic one.The electrical current of each spin component and the spin accumulation on the QD are calculated by using the nonequilibrium Green's function method.We find that in the Coulomb blockade regime,the current spin polarisation can reach 100%under a strong magnetic field.Meanwhile,the spin accumulation on the QD approaches to unit,and thus the dot is occupied by electrons of one certain spin orientation.The system can operate as a spin injector from a normal metal reservoir to a semiconductor material,and may find real usage in solid state quantum information processes.展开更多
We report on the single photon emission from single InAs/GaAs self-assembled Stranski-Krastanow quantum dots up to 80 K under pulsed and continuous wave excitations. At temperature 8OK, the second-order correlation fu...We report on the single photon emission from single InAs/GaAs self-assembled Stranski-Krastanow quantum dots up to 80 K under pulsed and continuous wave excitations. At temperature 8OK, the second-order correlation function at zero time delay, g^（2）（0）, is measured to be 0.422 for pulsed excitation. At the same temperature under continuous wave excitation, the photon antibunching effect is observed. Thus, our experimental results demonstrate a promising potential application of self-assembled InAs/GaAs quantum dots in single photon emission at liquid nitrogen temperature.展开更多
Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions...Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.展开更多
Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetr...Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetric PbTaS2 is a topological nodal line semimetal. In the absence of spin-orbit coupling （SOC）, one band inversion happens around a high symmetrical H point, which leads to forming a nodal line. The nodal line is robust and protected against gap opening by mirror reflection symmetry even with the inclusion of strong SOC. In addition, it also hosts exotic drumhead surface states either inside or outside the projected nodal ring depending on surface termination. The robust bulk nodal lines and drumhead-like surface states with SOC in PbTaS2 make it a potential candidate material for exploring the freakish properties of the topological nodal line fermions in condensed matter systems.展开更多
We report a photoluminescence （PL） energy red-shift of single quantum dots （QDs） by applying an in-plane compressive uniaxial stress along the [110] direction at a liquid nitrogen temperature. Uniaxial stress has ...We report a photoluminescence （PL） energy red-shift of single quantum dots （QDs） by applying an in-plane compressive uniaxial stress along the [110] direction at a liquid nitrogen temperature. Uniaxial stress has an effect not only on the confinement potential in the growth direction which results in the PL shift, but also on the cylindrical symmetry of QDs which can be reflected by the change of the full width at half maximum of PL peak. This implies that uniaxial stress has an important role in tuning PL energy and fine structure splitting of QDs.展开更多
We report the coherent resonant emission of the exciton state in a single InAs quantum dot,embedded in a planar optical microcavity.The quantum dot is excited by a laser beam from the cleaved sample edge,and the reson...We report the coherent resonant emission of the exciton state in a single InAs quantum dot,embedded in a planar optical microcavity.The quantum dot is excited by a laser beam from the cleaved sample edge,and the resonant fluorescence is collected in the direction perpendicular to the excitation laser beam,so the residual laser scattering can be deeply suppressed.This experimental setup enables us to observe Rabi oscillation and a Mollow triplet with Rabi energy up to about 27μeV.展开更多
We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadenin...We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadening and redshift. For ensemble quantum dots, however, the exciton emission peak shows narrowing and fast redshift. We use a simple steady-state rate equation model to simulate the experimental data of photoluminescence spectra. It is confirmed that carrier-phonon scattering gives the broadening of the exciton emission peak in single quantum dots while the effects of carrier thermal escape and retrapping play an important role in the narrowing and fast redshift of the exciton emission peak in ensemble quantum dots.展开更多
We theoretically investigate the single- and few-electron states in deformed HgTe quantum dots （QDs） with an inverted band structure using the full configuration interaction method. For the circular and deformed QD,...We theoretically investigate the single- and few-electron states in deformed HgTe quantum dots （QDs） with an inverted band structure using the full configuration interaction method. For the circular and deformed QD, it is found that the energy of edge states is robust against the shape from the circular QD in various elliptic ones. For the few electron states, electrons will firstly fill the edge states localized at the short axis, then the states localized at the long axis of the QD before filling the bulk states. The filling of the edge states can be controlled by tuning the dot size or the deformation of the geometry of the HgTe QD, respectively.展开更多
We investigate theoretically the carrier transport in a two-dimensional topological insulator of(001)HgTe/CdTe quantum-well heterostructure with inverted band,and find distinct switchable features of the transmission ...We investigate theoretically the carrier transport in a two-dimensional topological insulator of(001)HgTe/CdTe quantum-well heterostructure with inverted band,and find distinct switchable features of the transmission spectra in the topological edge states by designing the double-electric modulation potentials.The transmission spectra exhibit the significant Fabry–Pérot resonances for the double-electric transport system.Furthermore,the transmission properties show rich behaviors when the Fermi energy lies in the different locations in the energy spectrum and the double-electric barrier regions.The opacity and transparency of the double-modulated barrier regions can be controlled by tuning the modulated potentials,Fermi energy and the length of modulated regions.This electrical switching behavior can be realized by tuning the voltages applied on the metal gates.The Fabry–Pérot resonances leads to oscillations in the transmission which can be observed in experimentally.This electric modulated-mechanism provides us a realistic way to switch the transmission in edge states which can be constructed in low-power information processing devices.展开更多
We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distrib...We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topo- logical insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor.展开更多
We theoretically study the Casimir interaction between Weyl semimetals.When the distance a between semiinfinite Weyl semimetals is in the micrometer regime,the Casimir attraction can be enhanced by the chiral anomaly....We theoretically study the Casimir interaction between Weyl semimetals.When the distance a between semiinfinite Weyl semimetals is in the micrometer regime,the Casimir attraction can be enhanced by the chiral anomaly.The Casimir attraction depends sensitively on the relative orientations between the separations(b1,b2)of Weyl nodes in the Brillouin zone and show anisotropic behavior for the relative orientation of these separations(b1,b2)when they orient parallel to the interface.This anisotropy is quite larger than that in conventional birefringent materials.The Casimir force can be repulsive in the micrometer regime if the Weyl semimetal slabs are sufficiently thin and the direction of Weyl nodes separations(b1,b2)is perpendicular to the interface.The Casimir attraction between Weyl semimetal slabs decays slower than 1/a4 when the Weyl nodes separations b1 and b2 are both parallel to the interface.展开更多
By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots （QDs） with the configuration of positively charged excitons X＋ （one electron, two holes）...By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots （QDs） with the configuration of positively charged excitons X＋ （one electron, two holes）. The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.展开更多
We investigate the temperature dependence of photoluminescence （PL） and time-resolved PL on the metamorphic InGaAs quantum wells （QWs） with an emission wavelength of 1.55μm at room temperature. Time-resolved PL m...We investigate the temperature dependence of photoluminescence （PL） and time-resolved PL on the metamorphic InGaAs quantum wells （QWs） with an emission wavelength of 1.55μm at room temperature. Time-resolved PL measurements reveal that the optical properties can be partly improved by introducing antimony （Sb） as a surfactant during the sample growth. The temperature dependence of the radiative lifetime is measured, showing that for QWs grown with Sb assistance, the intrinsic exciton emission is dominated when the temperature is below 60K, while the nonradiative process becomes activated with further increases in temperature. However, without Sb assistance, the nonradiative centers are activated when the temperature is higher than 20 K.展开更多
We theoretically investigate the influence of both Rashba spin-orbit interaction(RSOI)and Dresselhaus spin-orbit interaction(DSOI)on electron spin states,electron distribution and the optical absorption of a quantum d...We theoretically investigate the influence of both Rashba spin-orbit interaction(RSOI)and Dresselhaus spin-orbit interaction(DSOI)on electron spin states,electron distribution and the optical absorption of a quantum dot.Our theoretical results show that the interplay between RSOI and DSOI results in an effective periodic potential,which consequently breaks the rotational symmetry and makes the quantum dot behave like two laterally coupled quantum dots.In the presence of RSOI and/or DSOI the spin is no longer a conserved quantity and its magnitude can be tuned by changing the strength of RSOI and/or DSOI.By reversing the direction of the perpendicular electric field,we can rotate the spatial distribution.This property provides us with a new way to control quantum states in a quantum dot by electrical means.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.92265203 and 11974340)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB0460000,XDB28000000,and XDPB22)+1 种基金the Chinese Academy of Sciences(Grant No.QYZDJSSW-SYS001)the National Key R&D Program of China(Grant No.2018YFA0306101).
文摘Based on the Gross–Pitaevskii equation,we theoretically investigate exciton Bose–Einstein condensation(BEC)in transition metal dichalcogenide monolayers(TMDC-MLs)under in-plane magnetic fields.We observe that the in-plane magnetic fields exert a strong influence on the exciton BEC wave functions in TMDC-MLs because of the mixing of the bright and dark exciton states via Zeeman effect.This leads to the brightening of the dark exciton BEC states.The competition between the dipole–dipole interactions caused by the long-range Coulomb interaction and the Zeeman effect induced by the in-plane magnetic fields can effectively regulate dark exciton BEC states.Our findings emphasize the utility of TMD-MLs as platforms for investigating collective phenomenon involving excited states.
基金supported by the National Natural Science Foundation of China(Grant Nos.92265203 and 11974340)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grants Nos.XDB0460000,XDB28000000,and XDPB22)+1 种基金the Innovation Program for Quantum Science and Technology(Grant No.2024ZD0300104)the National Key Research and Development Program of China(Grant No.2018YFA0306101)。
文摘Quasi-one-dimensional(1D)graphene nanoribbons(GNRs)play a crucial role in advancement of nextgeneration devices.Recent studies have suggested their potential to exhibit unique symmetry-protected topological phases defined by a Z_(2) invariant.By employing both the tight-binding model and the Floquet theory,our investigation demonstrates the effective control of the topological phase within quasi-1D armchair GNRs(AGNRs)using elliptically polarized light,unveiling rich topological phase diagrams.Specifically,we observe that varying the amplitude of the light can induce transitions in the band gap(E_(g))of AGNRs,leading to multiple changes in the system’s Z_(2) invariant.Furthermore,for heterojunctions composed of different AGNR segments,the junction state can be either created or eliminated by the application of elliptically polarized light.
基金the Natural Science Foundation of Shandong Province(Grant No.ZR2022MA053),the National Natural Science Foundation of China(Grant Nos.11704211,11847233,52301255,12205157,and 12205093)the Funda-mental Research Funds for the Central Universities(Grant No.lzujbky-2022-kb01)+2 种基金China and Germany Postdoctoral Exchange Program(Helmholtz-OCPC)China Postdoctoral Science Foundation(Grant No.2018M632608)Applied Basic Research Project of Qingdao(Grant No.18-2-2-16-jcb).
文摘The evolution process of magnetic domains in response to external fields is crucial for the modern understanding and application of spintronics.In this study,we investigated the domain rotation in stripe domain films of varying thicknesses by examining their response to microwave excitation in four different orientations.The resonance spectra indicate that the rotation field of stripe domain film under an applied magnetic field approaches the field where the resonance mode of sample changes.The saturation field of the stripe domain film corresponds to the field where the resonance mode disappears when measured in the stripe direction parallel to the microwave magnetic field.The results are reproducible and consistent with micromagnetic simulations,providing additional approaches and techniques for comprehending the microscopic mechanisms of magnetic domains and characterizing their rotation.
基金supported by the Natural Science Foundation of Fujian Province of China(Grant No.2020J01008)the National Natural Science Foundation of China(Grant No.12174382)。
文摘Janus WSSe monolayer is a novel two-dimensional(2D)material that breaks the out-of-plane mirror symmetry and has a large built-in electric field.These features lead to sizable Rashba spin-orbit coupling and enhanced nonlinear optical properties,making it a promising material platform for various spintronic and optoelectronic device applications.In recent years,nonlinear photocurrent responses such as shift and injection currents were found to be closely related to the quantum geometry and Berry curvature of materials,indicating that these responses can serve as powerful tools for probing the novel quantum properties of materials.In this work,we investigate the second-order nonlinear photocurrent responses in a Janus WSSe monolayer theoretically based on first-principles calculations and the Wannier interpolation method.It is demonstrated that the Janus WSSe monolayer exhibits significant out-of-plane nonlinear photocurrent coefficients,which is distinct from the nonJanus structures.Our results also suggest that the second-order nonlinear photocurrent response in the Janus WSSe monolayer can be effectively tuned by biaxial strain or an external electric field.Thus,the Janus WSSe monolayer offers a unique opportunity for both exploring nonlinear optical phenomena and realizing flexible 2D optoelectronic nanodevices.
基金Supported by the National Natural Science Foundation of China under Grant No 61274101Program for Liaoning Excellent Talents in University under Grant No 2009R01.
文摘We study electronic spin-polarised transport in a system composed of a quantum dot(QD)connected to one normal metal electrode and one ferromagnetic one.The electrical current of each spin component and the spin accumulation on the QD are calculated by using the nonequilibrium Green's function method.We find that in the Coulomb blockade regime,the current spin polarisation can reach 100%under a strong magnetic field.Meanwhile,the spin accumulation on the QD approaches to unit,and thus the dot is occupied by electrons of one certain spin orientation.The system can operate as a spin injector from a normal metal reservoir to a semiconductor material,and may find real usage in solid state quantum information processes.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60676054, 10734060 and 60625405, and the National Basic Research Programme of China under Grant No 2007CB924904, and the Knowledge Innovation Programme of Chinese Academy of Sciences under Grant No KJCX2.YW.W09-1.
文摘We report on the single photon emission from single InAs/GaAs self-assembled Stranski-Krastanow quantum dots up to 80 K under pulsed and continuous wave excitations. At temperature 8OK, the second-order correlation function at zero time delay, g^（2）（0）, is measured to be 0.422 for pulsed excitation. At the same temperature under continuous wave excitation, the photon antibunching effect is observed. Thus, our experimental results demonstrate a promising potential application of self-assembled InAs/GaAs quantum dots in single photon emission at liquid nitrogen temperature.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10474095 and 60625405
文摘Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.
基金Supported by the National Natural Science Foundation of China under Grant No 11504366the National Basic Research Program of China under Grant Nos 2015CB921503 and 2016YFE0110000
文摘Topological semimetals are a new type of matter with one-dimensional Fermi lines or zero-dimensional Weyl or Dirac points in momentum space. Here using first-principles calculations, we find that the non-centrosymmetric PbTaS2 is a topological nodal line semimetal. In the absence of spin-orbit coupling （SOC）, one band inversion happens around a high symmetrical H point, which leads to forming a nodal line. The nodal line is robust and protected against gap opening by mirror reflection symmetry even with the inclusion of strong SOC. In addition, it also hosts exotic drumhead surface states either inside or outside the projected nodal ring depending on surface termination. The robust bulk nodal lines and drumhead-like surface states with SOC in PbTaS2 make it a potential candidate material for exploring the freakish properties of the topological nodal line fermions in condensed matter systems.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60676054, and the National Key Projects for Basic Research of China under Grant No 2007CB924904.
文摘We report a photoluminescence （PL） energy red-shift of single quantum dots （QDs） by applying an in-plane compressive uniaxial stress along the [110] direction at a liquid nitrogen temperature. Uniaxial stress has an effect not only on the confinement potential in the growth direction which results in the PL shift, but also on the cylindrical symmetry of QDs which can be reflected by the change of the full width at half maximum of PL peak. This implies that uniaxial stress has an important role in tuning PL energy and fine structure splitting of QDs.
基金Supported by the National Natural Science Foundation of China under Grant Nos 90921015,11074246.
文摘We report the coherent resonant emission of the exciton state in a single InAs quantum dot,embedded in a planar optical microcavity.The quantum dot is excited by a laser beam from the cleaved sample edge,and the resonant fluorescence is collected in the direction perpendicular to the excitation laser beam,so the residual laser scattering can be deeply suppressed.This experimental setup enables us to observe Rabi oscillation and a Mollow triplet with Rabi energy up to about 27μeV.
基金Supported by the National Natural Science Foundation of China under Grant No 60676054, the Knowledge Innovation Project of Chinese Academy of Sciences （KJCX2.YW.W09-3）, and the National Basic Research Programme of China under Grant No 2007CB924904
文摘We investigate the temperature dependence of photoluminescence from single and ensemble InAs/GaAs quantum dots systematically. As temperature increases, the exciton emission peak for single quantum dot shows broadening and redshift. For ensemble quantum dots, however, the exciton emission peak shows narrowing and fast redshift. We use a simple steady-state rate equation model to simulate the experimental data of photoluminescence spectra. It is confirmed that carrier-phonon scattering gives the broadening of the exciton emission peak in single quantum dots while the effects of carrier thermal escape and retrapping play an important role in the narrowing and fast redshift of the exciton emission peak in ensemble quantum dots.
基金Supported by the National Natural Science Foundation of China under Grant No 11434010the National Basic Research Program of China under Grant No 2011CB922204
文摘We theoretically investigate the single- and few-electron states in deformed HgTe quantum dots （QDs） with an inverted band structure using the full configuration interaction method. For the circular and deformed QD, it is found that the energy of edge states is robust against the shape from the circular QD in various elliptic ones. For the few electron states, electrons will firstly fill the edge states localized at the short axis, then the states localized at the long axis of the QD before filling the bulk states. The filling of the edge states can be controlled by tuning the dot size or the deformation of the geometry of the HgTe QD, respectively.
基金Project supported by the College Innovation Project of Guangdong Province(Grant No.2020KTSCX329)the Social Public Welfare and Basic Research Project of Zhongshan City(Grant No.2020B2044)+2 种基金Zhongshan Polytechnic Highlevel Talents Project(Grant No.KYG2102)the National Key R&D Program of China(Grant No.2021YFA1200502)the National Natural Science Foundation of China(Grant No.12174423)。
文摘We investigate theoretically the carrier transport in a two-dimensional topological insulator of(001)HgTe/CdTe quantum-well heterostructure with inverted band,and find distinct switchable features of the transmission spectra in the topological edge states by designing the double-electric modulation potentials.The transmission spectra exhibit the significant Fabry–Pérot resonances for the double-electric transport system.Furthermore,the transmission properties show rich behaviors when the Fermi energy lies in the different locations in the energy spectrum and the double-electric barrier regions.The opacity and transparency of the double-modulated barrier regions can be controlled by tuning the modulated potentials,Fermi energy and the length of modulated regions.This electrical switching behavior can be realized by tuning the voltages applied on the metal gates.The Fabry–Pérot resonances leads to oscillations in the transmission which can be observed in experimentally.This electric modulated-mechanism provides us a realistic way to switch the transmission in edge states which can be constructed in low-power information processing devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.61076092 and 61290303)
文摘We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topo- logical insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor.
基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)the National Natural Science Foundation of China(Grant Nos.61674145,11974340,and 11504106)+1 种基金the National Key R&D Program of China(Grant Nos.2017YFA0303400 and 2018YFA0306101)the Chinese Academy of Sciences(Grant No.QYZDJ-SSW-SYS001 and XDPB22)。
文摘We theoretically study the Casimir interaction between Weyl semimetals.When the distance a between semiinfinite Weyl semimetals is in the micrometer regime,the Casimir attraction can be enhanced by the chiral anomaly.The Casimir attraction depends sensitively on the relative orientations between the separations(b1,b2)of Weyl nodes in the Brillouin zone and show anisotropic behavior for the relative orientation of these separations(b1,b2)when they orient parallel to the interface.This anisotropy is quite larger than that in conventional birefringent materials.The Casimir force can be repulsive in the micrometer regime if the Weyl semimetal slabs are sufficiently thin and the direction of Weyl nodes separations(b1,b2)is perpendicular to the interface.The Casimir attraction between Weyl semimetal slabs decays slower than 1/a4 when the Weyl nodes separations b1 and b2 are both parallel to the interface.
文摘By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots （QDs） with the configuration of positively charged excitons X＋ （one electron, two holes）. The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.
基金Supported by the National Natural Science Foundation of China under Grant No 60676054.
文摘We investigate the temperature dependence of photoluminescence （PL） and time-resolved PL on the metamorphic InGaAs quantum wells （QWs） with an emission wavelength of 1.55μm at room temperature. Time-resolved PL measurements reveal that the optical properties can be partly improved by introducing antimony （Sb） as a surfactant during the sample growth. The temperature dependence of the radiative lifetime is measured, showing that for QWs grown with Sb assistance, the intrinsic exciton emission is dominated when the temperature is below 60K, while the nonradiative process becomes activated with further increases in temperature. However, without Sb assistance, the nonradiative centers are activated when the temperature is higher than 20 K.
基金by the National Natural Science Foundation of China under Grant No 11004017.
文摘We theoretically investigate the influence of both Rashba spin-orbit interaction(RSOI)and Dresselhaus spin-orbit interaction(DSOI)on electron spin states,electron distribution and the optical absorption of a quantum dot.Our theoretical results show that the interplay between RSOI and DSOI results in an effective periodic potential,which consequently breaks the rotational symmetry and makes the quantum dot behave like two laterally coupled quantum dots.In the presence of RSOI and/or DSOI the spin is no longer a conserved quantity and its magnitude can be tuned by changing the strength of RSOI and/or DSOI.By reversing the direction of the perpendicular electric field,we can rotate the spatial distribution.This property provides us with a new way to control quantum states in a quantum dot by electrical means.
