Browsing by Author "Chen, L. Y."

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Dichotomy of photoinduced quasiparticle on CuO2 planes of YBa2Cu3O7 directly revealed by femtosecond polarization spectroscopy
(2007-08-01)
Luo, C. W.
;
Chen, L. Y.
;
Lee, Y. H.
;
Wu, K. H.
;
Juang, J. Y.
The dichotomy of photoinduced quasiparticle dynamics in the anisotropic high T, superconductors (YBa2CU3O7) is revealed by using the orientation-resolved ferntosecond reflection spectroscopy in the specially designed thin films. The transient reflectivity Delta R/R along the ab diagonal and b axis are totally different in the slow relaxation process which relates to the opening of the superconducting gap. In addition, the distribution of the temperature evolution of Delta R/R on the CuO2 planes of YBa2Cu3O7 may indicate the d-wave symmetry of the superconducting gap in high T, superconductors. (c) 2007 American Institute of Physics.
Ultrafast Dynamics of BiFeO(3) Thin Films Studied by Dual-Color Femtosecond Spectroscopy
(2011-01-01)
Chen, L. Y.
;
Yang, J. C.
;
Shih, H. C.
;
Liang, C. W.
;
Wu, T. -Y.
The ultrafast dynamics in (100)-oriented BiFeO(3) thin films were studied from 20 K to 300 K by using the dual-color femtosecond pump-probe spectroscopy, which were performed by the 400 nm (3.1 eV) pump pulses above the energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap of 2.67 eV. From the temperature-dependent transient reflectivity changes (Delta R/R), the anomalous changes were clearly observed below 200 K caused by magnons. Thus, the femtosecond pump-probe spectroscopy could unambiguously reveal the magnetization dynamics in BiFeO(3) with strong magnetoelectric coupling.
Ultrafast Dynamics of BiFeO3 Thin Films Studied by Dual-Color Femtosecond Spectroscopy
(2011-01-01)
Chen, L. Y.
;
Yang, J. C.
;
Shih, H. C.
;
Liang, C. W.
;
Wu, T. -Y.
The ultrafast dynamics in (100)-oriented BiFeO3 thin films were studied from 20 K to 300 K by using the dual-color femtosecond pump-probe spectroscopy, which were performed by the 400 nm (3.1 eV) pump pulses above the energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap of 2.67 eV. From the temperature-dependent transient reflectivity changes (Delta R/R), the anomalous changes were clearly observed below 200 K caused by magnons. Thus, the femtosecond pump-probe spectroscopy could unambiguously reveal the magnetization dynamics in BiFeO3 with strong magnetoelectric coupling.
Ultrafast photoinduced mechanical strain in epitaxial BiFeO3 thin films
(1970-01-01)
Chen, L. Y.
;
Yang, J. C.
;
Luo, C. W.
;
Laing, C. W.
;
Wu, K. H.
We studied ultrafast dynamics and photoinduced mechanical strain of BiFeO3 thin films by dual-color transient reflectivity measurements (Delta R/R). Anisotropic photostriction in BiFeO3 is found to be mainly driven by the optical rectification effect. Results of the photostriction at various thicknesses show that the estimated sound velocity along [110] direction of BiFeO3 is 4.76 km/s. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734512]
Ultrafast thermoelastic dynamics of HoMnO(3) single crystals derived from femtosecond optical pump-probe spectroscopy
(2011-05-03)
Shih, H. C.
;
Chen, L. Y.
;
Luo, C. W.
;
Wu, K. H.
;
Lin, J-Y
In this paper, the photo-induced ultrafast thermoelastic dynamics of hexagonal HoMnO(3) single crystals has been studied by using optical pump-probe spectroscopy. The thermoelastic effect in the ab-plane of hexagonal HoMnO3, associated with giant magnetoelastic coupling around the Neel temperature (T(N)), is intimately correlated to the emergence of a negative component in the transient reflectivity changes (Delta R/R) obtained in temperature-dependent pump-probe experiments. Moreover, the variation in the oscillation period in Delta R/R caused by a strain pulse propagating along the c-axis exhibits an abrupt drop around T(N), presumably due to the antiferromagnetic-ordering-induced changes in ferroelectricity.
Ultrafast thermoelastic dynamics of HoMnO3 single crystals derived from femtosecond optical pump-probe spectroscopy
(2011-05-03)
Shih, H. C.
;
Chen, L. Y.
;
Luo, C. W.
;
Wu, K. H.
;
Lin, J-Y
In this paper, the photo-induced ultrafast thermoelastic dynamics of hexagonal HoMnO3 single crystals has been studied by using optical pump-probe spectroscopy. The thermoelastic effect in the ab-plane of hexagonal HoMnO3, associated with giant magnetoelastic coupling around the Neel temperature (T-N), is intimately correlated to the emergence of a negative component in the transient reflectivity changes (Delta R/R) obtained in temperature-dependent pump-probe experiments. Moreover, the variation in the oscillation period in Delta R/R caused by a strain pulse propagating along the c-axis exhibits an abrupt drop around T-N, presumably due to the antiferromagnetic-ordering-induced changes in ferroelectricity.