Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan.
Phys Rev Lett. 2012 Nov 2;109(18):187002. doi: 10.1103/PhysRevLett.109.187002. Epub 2012 Oct 31.
Using terahertz (THz) pump-THz probe spectroscopy, we have investigated the dynamics of the nonequilibrium BCS state in a superconducting NbN film after the impulsive photoinjection of high-density Bogoliubov quasiparticles. The superconducting state rapidly changes within the duration of the monocycle THz pump pulse (1.6 ps). The complex optical conductivity spectrum in the nonequilibrium BCS state significantly deviates from that in the equilibrium state. The observed spectral features are qualitatively well described by the effective medium theory that assumes the formation of normal state patches embedded in a superconducting matrix.
利用太赫兹（THz）泵浦-太赫兹探针光谱技术，我们研究了在高密玻色子超快光注入后超导 NbN 薄膜中非平衡 BCS 态的动力学。在单周期太赫兹泵浦脉冲（1.6 ps）持续时间内，超导态迅速变化。非平衡 BCS 态的复光学导率谱明显偏离平衡态。所观察到的光谱特征可以用有效媒质理论很好地描述，该理论假设在超导矩阵中形成嵌入的正常态斑块。
