Browsing by Author "Wu, I. H."

Now showing 1 - 5 of 5

Doping dependence of the ultrafast electronic dynamics of Y(1-x)Pr(x)Ba(2)Cu(3)O(7-delta) thin-film superconductors from femtosecond optical spectroscopy
(2010-09-17)
Luo, C. W.
;
Lo, H. P.
;
Su, C. H.
;
Wu, I. H.
;
Chen, Y. -J.
Time-domain spectroscopy, which probes the dynamics of the electronic states near Fermi surface that are associated with superconductivity, has proven to be a powerful method for providing insights into the fundamental nature of both pseudogap and superconducting gap. This study shows that the unique T-x phase diagram with the time-evolving ultrafast dynamics of Y(1-x)Pr(x)Ba(2)Cu(3)O(7-delta) can be used to identify clearly the Nernst, pseudogap, and superconducting regions. All of the orders appear together at a specific delay time, such as 1.2-3 ps, after pumping by an ultrashort pulse. These discoveries suggest that the Nernst effect, the pseudogap and even superconductivity may have the same physical origin.
Doping dependence of the ultrafast electronic dynamics of Y1-xPrxBa2Cu3O7-delta thin-film superconductors from femtosecond optical spectroscopy
(2010-09-17)
Luo, C. W.
;
Lo, H. P.
;
Su, C. H.
;
Wu, I. H.
;
Chen, Y. -J.
Time-domain spectroscopy, which probes the dynamics of the electronic states near Fermi surface that are associated with superconductivity, has proven to be a powerful method for providing insights into the fundamental nature of both pseudogap and superconducting gap. This study shows that the unique T-x phase diagram with the time-evolving ultrafast dynamics of Y1-xPrxBa2Cu3O7-delta can be used to identify clearly the Nernst, pseudogap, and superconducting regions. All of the orders appear together at a specific delay time, such as 1.2-3 ps, after pumping by an ultrashort pulse. These discoveries suggest that the Nernst effect, the pseudogap and even superconductivity may have the same physical origin.
Quasiparticle Dynamics and Phonon Softening in FeSe Superconductors
(2012-06-20)
Luo, C. W.
;
Wu, I. H.
;
Cheng, P. C.
;
Lin, J. -Y.
;
Wu, K. H.
Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements (Delta R/R) provides unprecedented information on Fe-based superconductors. The amplitude of the fast component in Delta R/R clearly gives a competing scenario between spin fluctuations and superconductivity. Together with the transport measurements, the relaxation time analysis further exhibits anomalous changes at 90 and 230 K. The former manifests a structure phase transition as well as the associated phonon softening. The latter suggests a previously overlooked phase transition or crossover in FeSe. The electron-phonon coupling constant lambda is found to be 0.16, identical to the value of theoretical calculations. Such a small lambda demonstrates an unconventional origin of superconductivity in FeSe.
Quasiparticle Dynamics in FeSe Superconductors Studied by Femtosecond Spectroscopy
(2013-04-01)
Luo, C. W.
;
Wu, I. H.
;
Cheng, P. C.
;
Lin, J. -Y.
;
Wu, K. H.
The ultrafast quasiparticle dynamics in FeSe single crystals were measured by using dual-color transient reflectivity measurements (Delta R/R) from 4.4 to 290 K. In general, the typical Delta R/R of FeSe includes two significant components. One is the relaxation of photoinduced quasiparticles, which has been used to estimate the electron-phonon coupling strength (lambda=0.16). The other is the oscillation component due to the acoustic phonon. Moreover, the acoustic phonon's energy estimated from the period of oscillation in Delta R/R markedly shrinks around 90 K, which is the so-called phonon softening.
Ultrafast dynamics and phonon softening in Fe1+ySe1-xTex single crystals
(2012-10-31)
Luo, C. W.
;
Wu, I. H.
;
Cheng, P. C.
;
Lin, J-Y
;
Wu, K. H.
The ultrafast quasiparticle dynamics of Fe1+ySe1-xTex single crystals were investigated by dual-color transient reflectivity measurements (Delta R/R) from 4.3 to 290 K. The electron-phonon coupling strength lambda (= 0.16-0.01) and the temperature-dependent energy of longitudinal-acoustic phonons were, respectively, obtained from the relaxation time of a fast component and the period of an oscillation component in Delta R/R. Such a small lambda demonstrates the unconventional origin of superconductivity in FeSe. Moreover, the temperature-dependent Delta R/R exhibits anomalous changes at T-c, 90 K and 230 K, unambiguously revealing the phase transition as well as the phonon softening via the magnetoelastic effect.