Origin of negative thermal expansion in strongly correlatedf-electron systems

We have investigated the origin of the negative-thermal-expansion (NTE) phenomena observed in various strongly correlated f-electron systems, including Ce, Sm, and Yb rare-earth compounds and actinide element Pu. We have thoroughly surveyed existing nonmagnetic f-electron NTE materials and identified that the temperature (T)-induced valence transition plays an essential role in realizing the NTE in Sm-and Yb-based mixed-valence (MV) systems. We have discussed the contrasting thermal-expansion behaviors between (Sm, Yb)-based MV systems and their electron-hole symmetric counterparts (Ce, Eu)-based MV systems that exhibit positive-thermal-expansion (PTE) phenomena. We have also clarified the origin of intriguing thermal expansion behavior of Pu, which, upon cooling, reveals not only the NTE, but also the strong PTE. Fi-nally, we have predicted the possible existence of an additional NTE feature in topological-Kondo-insulator (TKI) candidates of SmB6, g-SmS, and YbB12 in the low-T regime where the TKI nature is expected to emerge.

Automated summary

We have investigated the origin of negative-thermal-expansion (NTE) in various f-electron systems and found that the valence transition induced by temperature is essential for realizing NTE in mixed-valence systems. We have discussed the contrasting thermal expansion behaviors between different systems and clarified the origin of intriguing thermal expansion behavior of Pu. We have also predicted the possible existence of additional NTE feature in topological-Kondo-insulator candidates in the low-T regime.