Evidence for a Second Order Phase Transition in Glasses at Very Low Temperatures -- 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.

4 pages, 4 figures, submitted to Phys. Rev. Lett

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