Non-classical dipoles in cold niobium clusters

TL;DR

This paper demonstrates that cold niobium clusters exhibit ferroelectric behavior with permanent electric dipoles at cryogenic temperatures, and that laser excitation can switch these dipoles off, revealing complex quantum states.

Contribution

It provides evidence against classical rotating dipole models and introduces a quantum state model for ferroelectric niobium clusters at low temperatures.

Findings

Niobium clusters have permanent electric dipoles at cryogenic temperatures.

Laser excitation can switch off the dipoles by inducing transitions between states.

Clusters exist in two states, with and without dipoles, depending on energy.

Abstract

Electric deflections of niobium clusters in molecular beams show that they have permanent electric dipole moments at cryogenic temperatures but not higher temperatures, indicating that they are ferroelectric. Detailed analysis shows that the deflections cannot be explained in terms of a rotating classical dipole, as claimed by Anderson et al. The shapes of the deflected beam profiles and their field and temperature dependences indicates that the clusters can exist in two states, one with a dipole and the other without. Cluster with dipoles occupy lower energy states. Excitations from the lower states to the higher states can be induced by low fluence laser excitation. This causes the dipole to vanish.