Soft Phonon Modes From Off-center Ge Atoms Lead To Ultralow ...

* Corresponding authors

a School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue 639798, Singapore E-mail: AlexYan@ntu.edu.sg

b Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA

c Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA

d Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA