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Negative Thermal Expansion in Cubic Ice: A Collective Quantum Effect of the hydrogen-bond network
Authors:
Loan Renaud,
Tomasz Poreba,
Richard Gaal,
A. Marco Saitta,
Michele Casula,
Livia Eleonora Bove
Abstract:
We report neutron powder diffraction measurements and path-integral molecular dynamics simulations of stacking-disorder-free cubic ice I$_c$, produced by topotactic degassing of C2 hydrogen hydrate. Across the cryogenic stability range, ice I$_c$ exhibits a density maximum near 70 K, closely matching that of hexagonal ice I$_h$ despite their different long-range stacking sequences. Negative therma…
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We report neutron powder diffraction measurements and path-integral molecular dynamics simulations of stacking-disorder-free cubic ice I$_c$, produced by topotactic degassing of C2 hydrogen hydrate. Across the cryogenic stability range, ice I$_c$ exhibits a density maximum near 70 K, closely matching that of hexagonal ice I$_h$ despite their different long-range stacking sequences. Negative thermal expansion in ice I is therefore not specific to hexagonal stacking, but arises from the shared open tetrahedral hydrogen-bond network. Simulations with the MB-pol potential quantitatively reproduce the experimental anomaly only when nuclear quantum effects are included. The density maximum coincides, within the temperature resolution, with maximal anisotropy of the proton quantum distribution. Neutron-derived displacement parameters independently reveal a strongly enhanced transverse proton displacement, while phonon calculations identify low-frequency transverse modes with the most negative Grüneisen parameters. Together, these results establish the negative thermal expansion of ice I as a collective quantum effect governed by nuclear statistics and the dynamics of the hydrogen-bond network.
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Submitted 30 July, 2026;
originally announced July 2026.
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Dual quantum locking: Dynamic coupling of hydrogen and water sublattices in hydrogen filled ice
Authors:
Loan Renaud,
Tomasz Poreba,
Simone Di Cataldo,
Alasdair Nicholls,
Léon Andriambariarijaona,
Maria Rescigno,
Richard Gaal,
Michele Casula,
A. Marco Saitta,
Livia Eleonora Bove
Abstract:
Hydrogen hydrates (HH) are a unique class of materials composed of hydrogen molecules confined within crystalline water frameworks. Among their multiple phases, the filled ice structures, particularly the cubic C2 phase, exhibit exceptionally strong host-guest interactions due to ultra-short H2-H2O distances and a 1:1 stoichiometry leading to two interpenetrated identical diamond-like sublattices,…
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Hydrogen hydrates (HH) are a unique class of materials composed of hydrogen molecules confined within crystalline water frameworks. Among their multiple phases, the filled ice structures, particularly the cubic C2 phase, exhibit exceptionally strong host-guest interactions due to ultra-short H2-H2O distances and a 1:1 stoichiometry leading to two interpenetrated identical diamond-like sublattices, one comprised of water molecules, the other of hydrogen molecules. At high pressures, nuclear quantum effects involving both hydrogen molecules and the water lattice become dominant, giving rise to a dual-lattice quantum system. In this work, we explore the sequence of pressure- and temperature-driven phase transitions in HH, focusing on the interplay between molecular rotation, orientational ordering, lattice symmetry breaking and hydrogen bond symmetrization. Using a combination of computational modeling based on classical and path-integral molecular dynamics,
quantum embedding, and high pressure experiments, including Raman spectroscopy and synchrotron X-ray diffraction at low temperatures and high pressures, we identify signatures of quantum-induced ordering and structural transformations in the C2 phase. Our findings reveal that orientational ordering in HH occurs at much lower pressures than in solid hydrogen, by inducing structural changes in the water network and enhancing the coupling of water and hydrogen dynamics. This work provides new insights into the quantum behavior of hydrogen under extreme mechanochemical confinement and establishes hydrogen-filled ices as a promising platform for the design of hydrogen-rich quantum materials.
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Submitted 29 October, 2025;
originally announced October 2025.
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Loss features in ultracold $^{162}$Dy gases: two- versus three-body processes
Authors:
Maxime Lecomte,
Alexandre Journeaux,
Loan Renaud,
Jean Dalibard,
Raphael Lopes
Abstract:
Dipolar gases like erbium and dysprosium have a dense spectrum of resonant loss features associated with their strong anisotropic interaction potential. These resonances display various behaviours with density and temperature, implying diverse microscopic properties. Here, we quantitatively investigate the low-field ($B < 6\,\text{G}$) loss features in ultracold thermal samples of $^{162}$Dy, reve…
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Dipolar gases like erbium and dysprosium have a dense spectrum of resonant loss features associated with their strong anisotropic interaction potential. These resonances display various behaviours with density and temperature, implying diverse microscopic properties. Here, we quantitatively investigate the low-field ($B < 6\,\text{G}$) loss features in ultracold thermal samples of $^{162}$Dy, revealing two- and three-body dominated loss processes. We investigate their temperature dependence and detect a feature compatible with a $d$-wave Fano-Feshbach resonance, which has not been observed before. We also analyse the expansion of the dipolar Bose-Einstein condensate as a function of the magnetic field and interpret the changes in size close to the resonances with a variation in the scattering length.
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Submitted 17 October, 2023;
originally announced October 2023.