Evidence for a Second Order Phase Transition in Glasses at Very Low Temperatures -- A Macroscopic Quantum State of Tunneling Systems

TL;DR

This study provides evidence of a second order phase transition in glasses at very low temperatures, suggesting the emergence of a macroscopic quantum state involving coherent tunneling systems.

Contribution

It reports the first experimental observation of a phase transition in glasses at millikelvin temperatures, indicating a collective quantum phenomenon.

Findings

Phase transition at 5.84 mK in BaO-Al2O3-SiO2 glass.

Magnetic field sensitivity of dielectric constant below transition.

Indications of a macroscopic quantum state of tunneling systems.

Abstract

Dielectric measurements at very low temperature indicate that in a glass with the eutectic composition BaO-Al$_2$O$_3$-SiO$_2$ a phase transition occurs at 5.84 mK. Below that temperature small magnetic fields of the order of 10 $\mu$T cause noticeable changes of the dielectric constant although the glass is insensitive to fields up to 20 T above 10 mK. The experimental findings may be interpreted as the signature of the formation of a new phase in which many tunneling systems perform a coherent motion resulting in a macroscopic wave function.