A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the groundstate energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy ...A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the groundstate energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy of the acoustic polarons in two and three dimensions are obtained. The 3D results agree with those obtained by using the Feynman path-integral approach. It is found that the critical coupling constant of the transition from the quasifree state to the self-trapped state in the 2D case is much smaller than in the 3D case for a given cutoff wave-vector. The theory has been used to judge the possibility of the self-trapping for several real materials. The results indicate that the self-trappings of the electrons in AlN and the holes in AlN and GaN are expected to be observed in 2D systems.展开更多
The inelastic scattering of oppositely charge polarons in polymer heterojunctions is believed to be of fundamental importance for the light-emitting and transport properties of conjugated polymers. Based on the tight-...The inelastic scattering of oppositely charge polarons in polymer heterojunctions is believed to be of fundamental importance for the light-emitting and transport properties of conjugated polymers. Based on the tight-binding SSH model, and by using a nonadiabatic molecular dynamic method, we investigate the effects of interface hopping on inelastic scattering of oppositely charged polarons in a polymer heterojunction. It is found that the scattering processes of the charge and lattice defect depend sensitively on the hopping integrals at the polymer/polymer interface when the interface potential barrier and applied electric field strength are constant. In particular, at an intermediate electric field, when the interface hopping integral of the polymer/polymer heterojunction material is increased beyond a critical value, two polarons can combine to become a lattice deformation in one of the two polymer chains, with the electron and the hole bound together, i.e., a self-trapped polaron-exciton. The yield of excitons then increases to a peak value. These results show that interface hopping is of fundamental importance and facilitates the formation of polaron-excitons.展开更多
The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.How...The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.However,these possibilities remain an open question in both theory and experiment.Here,theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects.First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state.Experimentally,ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals,but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals,highlighting the significance played by vacancy defects.Furthermore,the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ion dopants,due to enhancement of the exchange coupling between magnetic polarons.Room-temperature ferromagnetism is also observed in other LHPs,which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs,which is useful for future spintronic devices.展开更多
Electrical conductivity and dielectric properties of bismuth aluminate, Bi12.47Al0.53O19.5 （BAO）, were investigated in the frequency range from 1 Hz to 1 MHz in the temperature range from 420 K to 5 K. In the temper...Electrical conductivity and dielectric properties of bismuth aluminate, Bi12.47Al0.53O19.5 （BAO）, were investigated in the frequency range from 1 Hz to 1 MHz in the temperature range from 420 K to 5 K. In the temperature range from 360 K to 220 K the real part of the complex ac electrical conductivity and dielectric constant follow the universal dielectric response （UDR）, being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 360 K this mechanism governs the charge transport in this material. The characteristic parameters for polarons, W∞, ιo, and ι0 were determined.展开更多
The complex dielectric constant/ac electrical conductivity was investigated as a function offrequency and temperature in Pb_(5)Cr_(3)F_(19).The system undergoes a ferroelectric phase transition at higher temperatures....The complex dielectric constant/ac electrical conductivity was investigated as a function offrequency and temperature in Pb_(5)Cr_(3)F_(19).The system undergoes a ferroelectric phase transition at higher temperatures.At lower temperatures the real part of the complex ac electric conductivity was found to follow the universal dielectric response(UDR)σ′∝v^(s),typical for hopping or tunneling of localized charge carriers.A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that,at low temperatures,this mechanism governs the charge transport in Pb_(5)Cr_(3)F_(19).The value of the inverse attempt frequency τ0 indicates the femtosecond tunneling of polarons in the system similar to the Büttiker-Landauer transversal time.展开更多
基金Project supported by the Doctoral Program Foundation of Institutions of Higher Education China （Grant No 20040126003） and the Natural Science Foundation of Inner Mongol of China （Grant No 200408020101）.
文摘A 2D electron-longitudinal-acoustic-phonon interaction Hamiltonian is derived and used to calculate the groundstate energy of the acoustic polarons in two dimensions. The numerical results for the ground-state energy of the acoustic polarons in two and three dimensions are obtained. The 3D results agree with those obtained by using the Feynman path-integral approach. It is found that the critical coupling constant of the transition from the quasifree state to the self-trapped state in the 2D case is much smaller than in the 3D case for a given cutoff wave-vector. The theory has been used to judge the possibility of the self-trapping for several real materials. The results indicate that the self-trappings of the electrons in AlN and the holes in AlN and GaN are expected to be observed in 2D systems.
基金supported by the National Natural Science Foundation of China (Grant No. 11074064)the Key Project of the Ministry of Education of China (Grant No. 210021)the Natural Science Fund of Hebei Province of China (Grant No. A2010000357)
文摘The inelastic scattering of oppositely charge polarons in polymer heterojunctions is believed to be of fundamental importance for the light-emitting and transport properties of conjugated polymers. Based on the tight-binding SSH model, and by using a nonadiabatic molecular dynamic method, we investigate the effects of interface hopping on inelastic scattering of oppositely charged polarons in a polymer heterojunction. It is found that the scattering processes of the charge and lattice defect depend sensitively on the hopping integrals at the polymer/polymer interface when the interface potential barrier and applied electric field strength are constant. In particular, at an intermediate electric field, when the interface hopping integral of the polymer/polymer heterojunction material is increased beyond a critical value, two polarons can combine to become a lattice deformation in one of the two polymer chains, with the electron and the hole bound together, i.e., a self-trapped polaron-exciton. The yield of excitons then increases to a peak value. These results show that interface hopping is of fundamental importance and facilitates the formation of polaron-excitons.
基金Supported by National Natural Science Foundation of China(11547018)Research Foundation of Education Bureau of Hubei Province(Q20142706)+1 种基金Natural Science Foundation of Hubei Engineering University(z2013028)Natural Science Foundation of Hubei Province(2014CFB579)~~
基金This work was financially supported by NSFC(61725402)the Natural Science Foundation of Jiangsu Province(BK20190475).
文摘The possibility to induce a macroscopic magnetic moment in lead halide perovskites(LHPs),combined with their excellent optoelectronic properties,is of fundamental interest and has promising spintronic applications.However,these possibilities remain an open question in both theory and experiment.Here,theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects.First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state.Experimentally,ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals,but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals,highlighting the significance played by vacancy defects.Furthermore,the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ion dopants,due to enhancement of the exchange coupling between magnetic polarons.Room-temperature ferromagnetism is also observed in other LHPs,which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs,which is useful for future spintronic devices.
文摘Electrical conductivity and dielectric properties of bismuth aluminate, Bi12.47Al0.53O19.5 （BAO）, were investigated in the frequency range from 1 Hz to 1 MHz in the temperature range from 420 K to 5 K. In the temperature range from 360 K to 220 K the real part of the complex ac electrical conductivity and dielectric constant follow the universal dielectric response （UDR）, being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 360 K this mechanism governs the charge transport in this material. The characteristic parameters for polarons, W∞, ιo, and ι0 were determined.
基金Research was supported by the Slovenian Research Agency(P1-0125).
文摘The complex dielectric constant/ac electrical conductivity was investigated as a function offrequency and temperature in Pb_(5)Cr_(3)F_(19).The system undergoes a ferroelectric phase transition at higher temperatures.At lower temperatures the real part of the complex ac electric conductivity was found to follow the universal dielectric response(UDR)σ′∝v^(s),typical for hopping or tunneling of localized charge carriers.A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that,at low temperatures,this mechanism governs the charge transport in Pb_(5)Cr_(3)F_(19).The value of the inverse attempt frequency τ0 indicates the femtosecond tunneling of polarons in the system similar to the Büttiker-Landauer transversal time.
