Ice-Ih revisited: no proton tunneling observed in a quasielastic neutron scattering experiment

Significance of quantum effects in water has been well recognized. In particular, observation of a broad (~0.4 meV) quasielastic neutron scattering (QENS) signal in H₂O ice-Ih at T=5K [1] has attracted much attention. The QENS signal was explained by a model of concerted proton tunneling. There were a few attempts of theoretical understanding of the effect. Using path integral simulations, it was shown that quantum fluctuations in ice-Ih allow for collective tunneling of six protons in proton-ordered six rings [2]. However in [3] it was noted that concerted tunneling in ice-Ih should have very low frequency. In this study we performed QENS measurements of H₂O ice-Ih by using CNCS (T=1.7K) and BASIS (T=4K) spectrometers at SNS, with respective energy resolution similar to and 5 times better than the energy resolution in the original experiment [1]. We did not observe any QENS broadening, and the measured spectra for the ice-Ih and the reference vanadium sample were almost identical. Therefore, we conclude that there is no proton tunneling in ice-Ih at temperatures down to 1.7K measurable on energy scale 3 μeV and above.

1. L.E. Bove et al., Phys.Rev.Lett. 103 (2009) 165901.
2. C. Drechsel-Grau, D. Marx, Phys.Rev.Lett. 112 (2014) 148302.
3. L. Lin et al., J.Stat.Phys. 145 (2011) 365.