Fingerprints of Critical Phenomena in a Quantum Paraelectric Ensemble of Nanoconfined Water Molecules

We have studied the radio frequency dielectric response of a system consisting of separate polar water molecules periodically arranged in nanocages formed by the crystal lattice of the gemstone beryl. Below T = 20-30 K, quantum effects start to dominate the properties of the electric dipolar system as manifested by a crossover between the Curie-Weiss and the Barrett regimes in the temperature-dependent real dielectric permittivity epsilon '(T). When analyzing in detail the temperature evolution of the reciprocal permittivity (epsilon ')(-1) down to T approximate to 0.3 K and comparing it with the data obtained for conventional quantum paraelectrics, like SrTiO3, KTaO3, we discovered clear signatures of a quantum-critical behavior of the interacting water molecular dipoles: Between T = 6 and 14 K, the reciprocal permittivity follows a quadratic temperature dependence and displays a shallow minimum below 3 K. This is the first observation of dielectric fingerprints of quantum-critical phenomena in a paraelectric system of coupled point electric dipoles.

Automated summary

In this study, the radio frequency dielectric response of a system composed of water molecules arranged in nanocages was investigated. Quantum effects were found to dominate the properties of the electric dipolar system at low temperatures. By comparing with conventional quantum paraelectrics, clear signatures of quantum-critical behavior were observed.