Broad-band spectroscopy of nanoconfined water molecules

We have performed broad-band spectroscopic investigations of vibrational and relaxational excitations of water molecules confined to nanocages within artificial beryl and mineral cordierite crystals. Signatures of quantum critical phenomena within the H₂O molecular network are registered in beryl. In cordierite, a density functional analysis is applied to reconstruct the potential energy landscape experienced by H₂O molecules, revealing a pronounced anisotropy with a potential well of 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.