Twist mode in spherical alkali metal clusters

A remarkable orbital quadrupole magnetic resonance, so-called twist mode, i s predicted in alkali metal clusters where it is represented by I-pi = 2(-) low-energy excitations of valence electrons with strong M2 transitions to the ground state. We treat the twist by both macroscopic and microscopic wa ys. In the latter case, the shell structure of clusters is fully exploited, which is crucial for the considered size region (8 less than or equal to N -e less than or equal to 1314). The energy-weighted sum rule is derived for the pseudo-Hamiltonian. In medium and heavy spherical clusters, the twist dominates over its spin-dipole counterpart and becomes the most strong mult ipole magnetic mode.