Quantum Tunneling Drives Hydrogen Transport in Lanthanum Trihydride Near Practical Temperatures

by Riko Seibo
Tokyo, Japan (SPX) Apr 29, 2026
For decades, ion transport in solids has been described as a classical barrier-climbing process, in which an ion must acquire sufficient activation energy to surmount an energy barrier before it can migrate. For hydrogen -- the lightest element in the periodic table -- that classical picture can break down entirely.

Researchers from the Institute of Physics at the Chinese Academy of Sciences, Fudan University, and Peking University have now shown that hydrogen atoms in lanthanum trihydride (LaH3) can tunnel through energy barriers rather than always climbing over them. Using first-principles calculations grounded in ring-polymer instanton theory, the team identified a quantum mechanism governing hydrogen transport in the material.

For concerted migration -- in which multiple hydrogen atoms move cooperatively -- quantum tunneling becomes the dominant transport mechanism at approximately 71 K, a temperature close to that of liquid nitrogen. More strikingly, for single-ion migration, the crossover temperature rises to 308 K, placing quantum tunneling firmly within the near-room-temperature range.

Below each of these crossover temperatures, the instanton rate constants depart sharply from classical predictions, demonstrating that nuclear quantum effects in hydrogen transport are not confined to extreme cryogenic conditions but are relevant across far more practical operating regimes.

The study also resolves a longstanding mismatch between classical models and observed behavior. In classical descriptions, migration rate is governed primarily by barrier height. Once nuclear quantum effects are incorporated, barrier width becomes nearly as important. A narrow barrier is substantially more permeable to quantum tunneling than classical models would suggest, which explains why the difference in rate constant between concerted and single-ion pathways is dramatically overestimated when tunneling is ignored.

The calculations further reveal that the tunneling rate can be tuned by altering barrier geometry through the application of mechanical strain. This finding points to strain engineering as a practical strategy for controlling hydrogen motion in solid-state materials, with potential implications for the design of ionic conductors and hydrogen-storage compounds.

Taken together, the results establish a quantum framework for understanding hydrogen transport in LaH3 and identify unexpectedly high crossover temperatures at which quantum behavior dominates. The authors argue that nuclear quantum effects may need to be accounted for under far more commonplace conditions than the field has generally assumed, offering new theoretical grounding for the development and regulation of hydrogen-containing functional materials.

Research Report:Quantum tunneling dominates hydrogen migration in lanthanum trihydride near practical temperatures