Effects of acoustic plasmons in photoemission from coupled layered systems

We have studied photoemission in a quasi-two-dimensional solid consisting of coupled layers adopting the calculation in the limit of narrow hole band width. Unlike ordinary three-dimensional systems, gapless acoustic plasmons can be excited in the low energy regime. Combining the dielectric response of the coupled layers and the random phase approximation for a single layer, we can explicitly turn on or off the acoustic plasmon excitation. Through the comparison between the on- and off-acoustic calculations, acoustic plasmons in the photoemission spectra are found to suppress the quasiparticle weight and lead to an asymmetric broadening of the quasiparticle peak. Such tendencies are strengthened as the interlayer dielectric coupling increases. Further, the model is applied to the high-temperature superconductors and found to give additional asymmetric broadening to the pure two-dimensional spectra, which means that a significant part of the anomalously large inelastic background may be attributed to multiple intrinsic losses by acoustic plasmons.