Femtosecond Response of Quasiparticles and Phonons in Superconducting YBa 2 Cu 3 O 7-δ

1. Femtosecond Response of Quasiparticles and Phonons in Superconducting YBa2Cu3O7-δ A. Pashkin, M. Porer, M. Beyer, K. W. Kim, A. Dubroka, C. Bernhard, X. Yao, Y. Dagan, R. Hackl, A. Erb, J. Demsar, R. Huber, and A. Leitenstorfer PHYSICAL REVIEW LETTERS Vol:105 Article:067001 (2010) IppeiFujii Ashida Lab

2. Contents • Background • Introduction • Superconductivity • Optical conductivity of YBCO • Motivation • Experimental technique • Results • Summary • Future plan

3. Background T We can identify the motion of electron, ion and spin in solids by monitoring electromagnetic response It is difficult for strongly-correlated electron system

4. Background T For example, we can clarify correlation of electron and different elementary excitation by perturbation only electron system

5. Superconductivity 1911 Discovery of superconductivity 1957Resolution of BCS theory 1986 High-cuprate superconductor is rising rapidly

6. Optical conductivity σ1(ω) of YBCO Interplane conductivity is reduced by 1 order of magnitude Two phonon modes appear prominently Cu-O bond bending mode (peak at 39meV) Apical oxygen mode (peak at 71meV)

7. Motivation The origin of High-superconductor is discussed in long time BCS-type pairing fails to explain properties of SC cuprates. but Electron-phonon contributions is significant Monitor a detailed picture of the quasiparticlesand phonons

8. Optical pump-THz probe spectroscopy Pump pulse Pump pulse NIR-pulse 1.55eV , 0.3mJ/cm2 , 12fs Δt sample Probe pulse Probe pulse multi-THz pulse Probe pulse This technique enables to monitor ultrafast excitation and the relaxation( subpicosecond time resolution)

9. Dynamics of the photoinduced QP spectral weight as a function the delay time The time evolution of the change of the spectral weight = reaches its maximum with a delay of 150 fs Time resolution of this study is 40 fs First direct observation of the QP density generated during the pair cascade on the inherent time scale

10. 2D optical pump-THz probe data Broadband QP contribution featuring a similar spectral as E⊥c, and two narrow minima shows the same temporal trace as the in-plane conductivity In contrast The pumpinduced changes of the phonons are delayed Most striking difference

11. Optical conductivity and phenomenological model Phenomenological model : oscillator strength : damping constant : eigenfrequency : account for the asymmetry of the line shape below • The electronic contribution • The phonon contribution Discuss the fitting parameter below

12. Parameter A as a function of temperature The asymmetry decreases on heating and levels off above The asymmetry don’t vanish fully 100 300 0 200 Temperature (K)

13. Parameter A as a function of delay time The asymmetry vanish fully at 0.4 ps Find the difference between heating and optical excitation 0 3 1 2 Delay time (ps)

14. Summary • They measured midinfrared response of electrons and phonons in bulk YBCO after femtosecond excitation • The first direct observation of the QP density generated during the pair-breaking cascade on the inherent time scale • They find the effect of phonon-plasmon coupling by ultra fast spectroscopy for the first time

15. various pump frequency and wide band probe find various interaction in YBa2Cu3O7