Angstrom-scale interface modification extensively tunes thermodynamic ordering of strongly correlated protons in ice

The static and dynamic behaviour of strongly correlated many-body protons in nanoscale hydrogen-bond networks plays crucial roles in a wide range of physicochemical, biological and geological phenomena in nature. However, because of the difficulty of probing and manipulating the proton configuration in nanomaterials, controlling the cooperative behaviour of many-body protons remains challenging. By combining proton-order sensitive nonlinear optical spectroscopy and well-defined interface modification at molecular/atomic scale, we demonstrate the possibility of extensively tuning the emergent physical properties of strongly correlated protons beyond the thermodynamic constraints of bulk hydrogen bonds. Focusing on heteroepitaxially grown crystalline ice films as a model of a strongly correlated and frustrated proton system, we show that the emergence and disappearance of a high-Tc proton order on the nano- to mesoscale can be readily switched by angstrom-scale interface engineering. These results and concept are also applicable to other hydrogen-bonded materials, thus paving the way to the design and control of emergent properties of correlated proton systems.