Ferroelectricity in free niobium clusters

Electric deflections of gas-phase, cryogenically cooled, neutral niobium clusters [Nb-N; number of atoms (N) = 2 to 150, temperature (T) = 20 to 300 kelvin], measured in molecular beams, show that cold clusters may attain an anomalous component with very large electric dipole moments. In contrast, room- temperature measurements show normal metallic polarizabilities. Characteristic energies k(B)T(G)(N) [Boltzmann constant k(B) times a transition temperature T-G(N)] are identified, below which the ferroelectric-like state develops. Generally, T-G decreases [110 > T-G(N) > 10 K] as N increases, with pronounced even-odd alternations for N > 38. This new state of metallic matter may be related to bulk superconductivity.