One-Dimensional Fluctuations and the Chain-Ordering Transformation inHg3−δAsF6

Neutron-scattering behavior and other properties of the mercury chains in ${\mathrm{Hg}}_{3-\delta }\mathrm{As}{\mathrm{F}}_6$ are calculated from a simple microscopic model. The independent chains satisfy a quantum sine-Gordon equation. The theory accounts for existing observations and makes a number of testable predictions about properties of the disordered phase, the nature of the phase transition, evolution of long-range order, and the excitation spectrum at low temperatures.