Prediction of thermally driven quasi-1D superionic states in carbon hydride under giant planetary conditions

Abstract Planetary interiors experience high-pressure-high temperature conditions that give rise to unconventional states of matter, reshaping our understanding of planetary dynamics and the generation of magnetic fields. Here, using first-principles computational simulations in combination with machine-learning interatomic potentials, we predict a distinct atomic state, termed a quasi-1D superionic phase, that emerges in a stable carbohydride (CH) compound under giant planetary interior conditions. This phase originates from temperature-induced transformations and features a chiral carbon framework intertwined with dynamic hydrogen helices. At 0 K, electronic redistribution along the hydrogen sublattice induces metallization. In contrast, upon heating, carbon atoms form a rigid lattice, and hydrogen exhibits rotational motion in the x y-plane and diffusion along the z-axis, resulting in anisotropic mobility. A high-pressure-temperature phase diagram reveals sequential transitions from solid to quasi-1D superionic, 3D superionic, and fluid states. The quasi-1D superionic CH phase exhibits pronounced anisotropy in electronic, thermal, and ionic conductivity, with electronic transport predominating and the ionic contribution remaining negligible. This anisotropic behavior provides a microscopic mechanism for directional energy and charge transport under high-pressure and high-temperature conditions, offering insight into how structural anisotropy can govern transport properties in materials subjected to ultra-high pressures. This anisotropic behavior provides a microscopic mechanism for directional energy and charge transport under extreme conditions, offering new insights into the behavior of high-pressure materials and magnetic phenomena in giant and sub-Neptune exoplanets.