Ferroelectricity in Free Niobium Clusters

Abstract

Electric deflections of gas-phase, cryogenically cooled, neutral niobium clusters [Nb N ; number of atoms ( N ) = 2 to 150, temperature ( T ) = 20to 300kelvin], 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 ) > 10K] as N increases, with pronounced even-odd alternations for N > 38. This new state of metallic matter may be related to bulk superconductivity.