Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herei...Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herein,we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd_(3)As_(2)utilizing time-resolved optical pump-terahertz probe spectroscopy.Comparing to the pristine Cd_(3)As_(2),we found that the relaxation time of the lightly doped alloy is slightly shorter,while that of the heavily doped alloy exhibits a significant prolongation.Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase,the photocarrier dynamics are dominated by the cooling of Dirac fermions.In heavily doped alloy,however,the observed longer relaxation process can be attributed to interband electron-hole recombination,which is a result of doping-induced transition into a trivial semiconductor phase.Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd_(3)As_(2),and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications.展开更多
We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride(PtTe2)thin films via femtosecond(fs)pump-probe spectroscopy at room temperature.Quantitative...We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride(PtTe2)thin films via femtosecond(fs)pump-probe spectroscopy at room temperature.Quantitative analysis revealed that the incoherent electronic relaxation consists of two components:a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds(ps).Furthermore,the launch of a coherent acoustic phonon(CAP)in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave.The sound velocity and Young’s modulus in the thick PtTe_(2) are determined to be 1.736 km/s and 29.5 GPa,respectively.In addition,the coherent optical phonon(COP)with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films,which is ascribed to displacive excitation of coherent phonon(DECP).The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2.Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’recovery pathway and lifetimes in PtTe_(2).Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations,which may find applications in the fields of optoelectronics and ultrafast photonics.展开更多
基金National Natural Science Foundation of China(12404396,92150101,52225207,52350001)China Postdoctoral Science Foundation(2024M751932)Postdoctoral Fellowship Program of CPSF(GZB20240418)。
文摘Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herein,we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd_(3)As_(2)utilizing time-resolved optical pump-terahertz probe spectroscopy.Comparing to the pristine Cd_(3)As_(2),we found that the relaxation time of the lightly doped alloy is slightly shorter,while that of the heavily doped alloy exhibits a significant prolongation.Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase,the photocarrier dynamics are dominated by the cooling of Dirac fermions.In heavily doped alloy,however,the observed longer relaxation process can be attributed to interband electron-hole recombination,which is a result of doping-induced transition into a trivial semiconductor phase.Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd_(3)As_(2),and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications.
基金National Natural Science Foundation of China(61735010,92150101,11774233,62122036,61974176).
文摘We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride(PtTe2)thin films via femtosecond(fs)pump-probe spectroscopy at room temperature.Quantitative analysis revealed that the incoherent electronic relaxation consists of two components:a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds(ps).Furthermore,the launch of a coherent acoustic phonon(CAP)in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave.The sound velocity and Young’s modulus in the thick PtTe_(2) are determined to be 1.736 km/s and 29.5 GPa,respectively.In addition,the coherent optical phonon(COP)with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films,which is ascribed to displacive excitation of coherent phonon(DECP).The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2.Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’recovery pathway and lifetimes in PtTe_(2).Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations,which may find applications in the fields of optoelectronics and ultrafast photonics.
