A Variety of Giant Resonances in Metal Clusters

Metal cluster (MC) is a bound system consisting of atoms of some metal. The amount of atoms can vary from a few to many thousands. Some MC, mainly of alkali (Li, K, Na, ...) and noble (Ag, Au, ...) metals, demonstrate a striking similarity to atomic nuclei (see reviews). In these clusters the valence electrons are weakly coupled to the ions and, like nucleons in nuclei, are not strongly localized. The mean free path of valence electrons is of the same order of magnitude as the size of the cluster. This favors the valence electrons to form a mean field of the same kind as in nuclei (with the similar shell structure and magic numbers). In addition to the mean field, MC demonstrate other similarities with atomic nuclei: deformation in the case of open shells, variety of giant resonances (GR), fission, etc.. As a result, many theoretical ideas and methods of nuclear physics can, after a certain modification, be applied to MC . This review is devoted to collective oscillations of valence electrons in MC. Valence electrons can be considered as the counterparts of nucleons in nuclei, and their oscillations as the counterparts of nuclear GR. Investigation of GR in MC is interesting in two aspects: it allows to understand deeper general properties of collective modes in finite Fermi systems and, simultaneously, allows to study striking peculiarities of MC. GR in clusters and atomic nuclei are well overlapped. However, some specific properties of MC cause considerable differences in the behavior of GR in these two systems. For example: the