Photoexcitation-Induced Nonthermal Ultrafast Loss of Long-Range Order in GeTe

Nonadiabatic quantum molecular dynamics is used to investigate the evolution of GeTe photoexcited states. Results reveal a photoexcitation-induced picosecond nonthermal path for the loss of long-range order. A valence electron excitation threshold of 4% is found to trigger local disorder by switching Ge atoms from octahedral to tetrahedral sites and promoting Ge-Ge bonding. The resulting loss of long-range order for a higher valence electron excitation fraction is achieved without fulfilling the Lindemann criterion for melting, therefore utilizing a nonthermal path. The photoexcitation-induced structural disorder is accompanied by charge transfer from Te to Ge, Ge-Te bonding-to-antibonding, and Ge-Ge antibonding-to-bonding change, triggering Ge-Te bond breaking and promoting the formation of Ge-Ge wrong bonds. These results provide an electronic-structure basis to understand the photoexcitation-induced ultrafast changes in the structure and properties of GeTe and other phase-change materials.

Automated summary

Nonadiabatic quantum molecular dynamics is used to investigate the evolution of photoexcited states in GeTe. Results reveal a nonthermal path for the loss of long-range order induced by photoexcitation, which triggers local disorder and promotes the formation of wrong bonds. These findings provide an electronic-structure basis for understanding the ultrafast changes in the structure and properties of GeTe and other phase-change materials induced by photoexcitation.