title: Anomalous lattice dynamics near the ferroelectric instability in PbTe.
abstract: A recent report of highly unusual ferroelectric fluctuations in PbTe by E. S. Božin et al. [Science 330, 1660 (2010)] raises fundamental questions about the nature of underlying lattice dynamics. We show by first-principles calculations that the reported results can be attributed to abnormally large-amplitude thermal vibrations that stem from a delicate competition of dual ionicity and covalency, which puts PbTe near ferroelectric instability. It produces anomalous properties such as partially localized low-frequency phonon modes, a soft transverse optical phonon mode, and a positive temperature coefficient for the band gap. These results account for experimental findings and resolve the underlying atomistic mechanisms, which have broad implications for materials near dynamic instabilities.
authors: Department of Physics and HiPSEC, University of Nevada, Las Vegas, Nevada 89154, USA.
authors: Yi
authors: Y
authors: Zhang
authors: Xuezhi
authors: X
authors: Ke
authors: Paul R C
authors: PR
authors: Kent
authors: Jihui
authors: J
authors: Yang
authors: Changfeng
authors: C
authors: Chen