Theory of ultrafast pump-probe phenomena in high-temperature superconductors*

The physics underlying the pairing mechanism for high-temperature superconductors remains a topic of current interest. The complexity lies with the existence of competing interactions in these strongly correlated electronic materials. The ultra-fast pump-probe technique can make a stride to untangle the competing degrees of freedom (DOF). In this talk, the theoretical underpinning for this technique will be reviewed. In particular, we have developed a three-temperature model [1] to simulate the real time dependence of the electron and phonon temperatures in high-temperature superconductors. The model considers anisotropic electron-phonon coupling [2]. Based on this model, we have calculated the time-resolved spectral function, which exhibits interesting features with time delay. It has been found that the excitation of phononic DOF can provide a defining signature for the evidence of electron-vibration mode coupling [1]. In addition, the time-resolved optical conductivity and Raman spectra will also be discussed within the same model [3]\\[4pt] [1] Jianmin Tao and Jian-Xin Zhu, Phys. Rev. B \textbf{81}, 224506 (2010);\\[0pt] [2] T. P. Devereaux \textit{et al}., Phys. Rev. Lett. \textbf{93}, 117004 (2004); Jian-Xin Zhu \textit{et al.}, Phys. Rev. Lett. \textbf{97}, 177001 (2006);\\[0pt] [3] Jianmin Tao and Jian-Xin Zhu \textit{et al}., unpublished (2010).