Origin of negative thermal expansion in strongly correlatedf-electron systems

Abstract

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.