Despite simple chemical structure and its importance in our life, water remains one of the most puzzling liquids. Its behavior in the “no-man’s land” (between 240K and 150K), structural relaxation at low temperatures and even the glass transition temperature Tg continue to be the topic of active discussions. In this talk we will present an overview of anomalous properties of supercooled water and putative ideas suggested for their explanations. We will present dielectric relaxation data that show unphysically weak temperature dependence of structural relaxation in water at temperatures close to its Tg~136K. Next, we will show that quantum effects play an important role in the dynamics of deeply supercooled water. Based on the recent theoretical idea [1], we analyze neutron scattering and dielectric relaxation spectroscopy data. This analysis indeed reveals that quantum fluctuations are not negligible and can explain well the unusual behavior of structural relaxation in supercooled water at temperatures close to Tg. Moreover, the quantum effects can also explain the apparent “Fragile-to-Strong Crossover” observed in dynamics of supercooled water at T~200-170K. These results have significant implications for our understanding of water dynamics and its peculiar behavior at low temperatures. In broader aspects, it might also influence our view on dynamics of other low-Tg liquids. Traditionally quantum effects are neglected when discussing relaxation dynamics of supercooled liquids. The present results clearly emphasize that quantum fluctuations can play an important role in the dynamics of liquids consisting of light molecules.
[1] V.N. Novikov, A.P. Sokolov, Phys. Rev. Letters 110, 065701 (2013)