Broad-Band Spectroscopy of Nanoconfined Water Molecules

We have performed broad-band spectroscopic investigations of vibrational and relaxational excitations of water molecules confined to nanocageswithin artificial beryl and mineral cordieritecrystals. Signatures of quantum critical phenomenawithin the H2O molecular network are registered in beryl. In cordierite, a density functional analysis is applied to reconstruct the potential energy landscapeexperienced by H2O molecules, revealing a pronounced anisotropy with a potential wellof about 10 meV for the molecular dipole moment aligned along the b-axis. This anisotropy leads to a strongly temperature dependent and anisotropic relaxational response of the dipoles at radiofrequencies with the activation energies corresponding to the barriers of the rotational potential. At T ≈ 3 K, we identify signatures of a transition into a glassy state composed by clusters of H2O dipoles. Rich set of anisotropic and temperature-dependent excitations are observed in the terahertz frequency range which we associate with rotational/translational vibrations.