High-Pressure Synthesis of Magnetic Neodymium Polyhydrides
Di Zhou, Dmitrii V. Semenok, Hui Xie, Xiaoli Huang, Defang Duan, Alex Aperis, Peter M. Oppeneer, Michele Galasso, Alexey I. Kartsev, Alexander G. Kvashnin, Artem R. Oganov, Tian Cui
Abstract
Ongoing search for room-temperature superconductivity is inspired by the unique properties of the electron–phonon interaction in metal superhydrides. Encouraged by the recently found highest- T C superconductor fcc -LaH 10, here we discover several superhydrides of another lanthanoid, neodymium. We identify three novel metallic Nd–H phases at pressures ranging from 85 to 135 GPa: I 4/ mmm -NdH 4, C 2/ c -NdH 7, and P 6 3 / mmc -NdH 9, synthesized by laser-heating metal samples in NH 3 BH 3 media for in situ generation of hydrogen. A lower trihydride Fm 3̅ m -NdH 3 is found at pressures from 2 to 52 GPa. I 4/ mmm -NdH 4 and C 2/ c -NdH 7 are stable from 135 to 85 GPa, and P 6 3 / mmc -NdH 9 is stable from 110 to 130 GPa. Measurements of the electrical resistance of NdH 9 demonstrate a possible superconducting transition at ∼4.5 K in P 6 3 / mmc -NdH 9 . Our theoretical calculations predict that all of the neodymium hydrides have antiferromagnetic order at pressures below 150 GPa and represent one of the first discovered examples of strongly correlated superhydrides with large exchange spin-splitting in the electronic band structure (>450 meV). The critical Néel temperatures for new neodymium hydrides are estimated using the mean-field approximation to be about 4 K (NdH 4 ), 251 K (NdH 7 ), and 136 K (NdH 9 ).