Center for Integrated Science and Engineering, Columbia University, New York, New York 10027, USA.
Phys Rev Lett. 2010 Jul 2;105(1):017602. doi: 10.1103/PhysRevLett.105.017602. Epub 2010 Jul 1.
We demonstrate angle-resolved, tunable, two-photon photoemission (2PPE) to map a bulk unoccupied band, viz. the Cu sp band 0 to 1 eV below the vacuum level, in the vicinity of the L point. This short-lived bulk band is seen due to the strong optical pump rate, and the observed transition energies and their dispersion with photon energy ℏω, are in excellent agreement with tight-binding band-structure calculations. The variation of the final-state energy with ℏω has a measured slope of ∼1.64 in contrast to values of 1 or 2 observed for 2PPE from two-dimensional states. This unique variation illustrates the significant role of the perpendicular momentum ℏk_{⊥} in 2PPE.
我们展示了角度分辨、可调谐的双光子光发射（2PPE），以绘制体非占据带的图，即导带以下 0 到 1 eV 的 Cu sp 带，在 L 点附近。由于强的光泵浦速率，可以看到这个寿命短的体带，并且观察到的跃迁能量及其与光子能量 ħω的色散，与紧束缚能带结构计算非常吻合。与二维态的 2PPE 观察到的 1 或 2 值相比，终态能量随 ħω的变化的测量斜率约为 1.64。这种独特的变化说明了垂直动量 ħk_{⊥}在 2PPE 中的重要作用。
