Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering ra...Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing.The plasma edge shows a slight blue shift upon cooling,similar to the behavior of Cu_(x)Bi_(2)Se_(3).As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature,the effective mass is proved to increase as well,which is in contrast with that of Cu_(x)Bi_(2)Se_(3).We also perform the ultrafast pump-probe study on the Sr_(0.2)Bi_(2)Se_(3)compounds.Resembling its parent compound Bi_(2)Se_(3),three distinct relaxation processes are found to contribute to the transient reflectivity.However,the deduced relaxation times are quite different.In addition,the electron-optical-phonon coupling constant is identified to beλ=0.88.展开更多
Time-resolved photoluminescence(TRPL)has been extensively used to measure the carrier lifetime in lead halide perovskites.The TRPL curves of perovskite materials are usually fitted with a multi-exponential function,in...Time-resolved photoluminescence(TRPL)has been extensively used to measure the carrier lifetime in lead halide perovskites.The TRPL curves of perovskite materials are usually fitted with a multi-exponential function,instead of a single exponential one.This was considered to be a result of the surface and the bulk recombination or the additional radiative recombination caused by the high excited carrier density.Here,a new model considering the diffusion and the trap-assisted recombination of carriers is proposed to explain the TRPL curves.The expressions of the TRPL curves and the transient absorption(TA)dynamic curves are theoretically derived,demonstrating that the TRPL curve is an infinite exponential series,regardless of the presence of surface recombination or not.Our newly developed highly sensitive nanosecond TA and TRPL were employed to measure the carrier dynamics of the same sample under low illumination in the linear response region of TA,thereby experimentally verifying our model.These results suggest that the decay of the TRPL is not only a consequence of the carrier recombination but also the carrier diffusion.TRPL cannot provide a direct measurement of the carrier lifetime,whereas TA spectroscopy can.Furthermore,the surface and the bulk recombination can be resolved and the average diffusion coefficient(D)can also be correctly obtained by combining TRPL and TA measurements.We also propose an approximate method for calculating the carrier lifetime and diffusion coefficient of high-quality perovskite films.Our model provides not only a new interpretation of the dynamics of the PL decay but also a deep insight into the carrier dynamics in the nanosecond time scale under working condition of perovskites solar cells.展开更多
We perform an in-plane optical spectroscopy measurement on high quality Fe Se single crystals grown by a vapor transport technique. Below the structural transition at Ts 90 K, the reflectivity spectrum clearly shows a...We perform an in-plane optical spectroscopy measurement on high quality Fe Se single crystals grown by a vapor transport technique. Below the structural transition at Ts 90 K, the reflectivity spectrum clearly shows a gradual suppression around 400 cm 1and the conductivity spectrum shows a peak at higher frequency. The energy scale of this gap-like feature is comparable to the width of the band splitting observed by ARPES. The low-frequency conductivity consists of two Drude components and the overall plasma frequency is smaller than that of the Fe As based compounds, suggesting a lower carrier density or stronger correlation effect. The plasma frequency becomes even smaller below Tswhich agrees with the very small Fermi energy estimated by other experiments. Similar to iron pnictides, a clear temperature-induced spectral weight transfer is observed for Fe Se, being indicative of strong correlation effect.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074042 and 11704033)the National Key Research and Development Program of China(Grant Nos.2021YFA1400400 and 2016YFA0302300)the Fundamental Research Funds for the Central Universities。
文摘Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing.The plasma edge shows a slight blue shift upon cooling,similar to the behavior of Cu_(x)Bi_(2)Se_(3).As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature,the effective mass is proved to increase as well,which is in contrast with that of Cu_(x)Bi_(2)Se_(3).We also perform the ultrafast pump-probe study on the Sr_(0.2)Bi_(2)Se_(3)compounds.Resembling its parent compound Bi_(2)Se_(3),three distinct relaxation processes are found to contribute to the transient reflectivity.However,the deduced relaxation times are quite different.In addition,the electron-optical-phonon coupling constant is identified to beλ=0.88.
基金This work was supported by the National Key Basic Research Program of China(2021YFA0718700,2017YFA0302900,2017YFA0303003,2018YFB0704102,and 2018YFA0305800)the National Natural Science Foundation of China(11888101,11927808,11834016,11961141008,12174428,and 12274439)+4 种基金the Strategic Priority Research Program(B)of Chinese Academy of Sciences(XDB25000000,XDB33000000)CAS Interdisciplinary Innovation Team,Beijing Natural Science Foundation(Z190008)CAS through the Youth Innovation Promotion Association(2022YSBR-048)Key-Area Research and Development Program of Guangdong Province(2020B0101340002)the Center for Materials Genome.
基金supported by the National Natural Science Foundation of China(Grant No.11888101)National Key Research and Development Program of China(Grant No.2022YFA1403901)+1 种基金Sichuan Science and Technology Program(Grant Nos.2021JDTD0021,and 2022ZYD0015)Innovation Funds from China Academy of Engineering Physics(Grant No.CX20210037)。
文摘Time-resolved photoluminescence(TRPL)has been extensively used to measure the carrier lifetime in lead halide perovskites.The TRPL curves of perovskite materials are usually fitted with a multi-exponential function,instead of a single exponential one.This was considered to be a result of the surface and the bulk recombination or the additional radiative recombination caused by the high excited carrier density.Here,a new model considering the diffusion and the trap-assisted recombination of carriers is proposed to explain the TRPL curves.The expressions of the TRPL curves and the transient absorption(TA)dynamic curves are theoretically derived,demonstrating that the TRPL curve is an infinite exponential series,regardless of the presence of surface recombination or not.Our newly developed highly sensitive nanosecond TA and TRPL were employed to measure the carrier dynamics of the same sample under low illumination in the linear response region of TA,thereby experimentally verifying our model.These results suggest that the decay of the TRPL is not only a consequence of the carrier recombination but also the carrier diffusion.TRPL cannot provide a direct measurement of the carrier lifetime,whereas TA spectroscopy can.Furthermore,the surface and the bulk recombination can be resolved and the average diffusion coefficient(D)can also be correctly obtained by combining TRPL and TA measurements.We also propose an approximate method for calculating the carrier lifetime and diffusion coefficient of high-quality perovskite films.Our model provides not only a new interpretation of the dynamics of the PL decay but also a deep insight into the carrier dynamics in the nanosecond time scale under working condition of perovskites solar cells.
基金supported by the National Natural Science Foundation of China(11120101003,11327806)the National Basic Research Program of China(2012CB821403)
文摘We perform an in-plane optical spectroscopy measurement on high quality Fe Se single crystals grown by a vapor transport technique. Below the structural transition at Ts 90 K, the reflectivity spectrum clearly shows a gradual suppression around 400 cm 1and the conductivity spectrum shows a peak at higher frequency. The energy scale of this gap-like feature is comparable to the width of the band splitting observed by ARPES. The low-frequency conductivity consists of two Drude components and the overall plasma frequency is smaller than that of the Fe As based compounds, suggesting a lower carrier density or stronger correlation effect. The plasma frequency becomes even smaller below Tswhich agrees with the very small Fermi energy estimated by other experiments. Similar to iron pnictides, a clear temperature-induced spectral weight transfer is observed for Fe Se, being indicative of strong correlation effect.
