Evidence for the weakly coupled electron mechanism in an Anderson-Blount polar metal

• Published in: Nature communications 2019-07, Vol.10 (1), p.3217-7, Article 3217
• Main Authors: Laurita, N. J., Ron, A., Shan, Jun-Yi, Puggioni, D., Koocher, N. Z., Yamaura, K., Shi, Y., Rondinelli, J. M., Hsieh, D.
• Format: Article
• Language: English
• Subjects: 140/125; 639/624/400/584; 639/766/119/2795; 639/766/119/996; Ferroelectric materials; Ferroelectricity; Humanities and Social Sciences; MATERIALS SCIENCE; Metals; multidisciplinary; Phase transitions; Phonons; Science; Science (multidisciplinary); Specific heat; Spectroscopy
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-11172-2

Over 50 years ago, Anderson and Blount proposed that ferroelectric-like structural phase transitions may occur in metals, despite the expected screening of the Coulomb interactions that often drive polar transitions. Recently, theoretical treatments have suggested that such transitions require the itinerant electrons be decoupled from the soft transverse optical phonons responsible for polar order. However, this decoupled electron mechanism (DEM) has yet to be experimentally observed. Here we utilize ultrafast spectroscopy to uncover evidence of the DEM in LiOsO 3, the first known band metal to undergo a thermally driven polar phase transition ( T c  ≈ 140 K). We demonstrate that intra-band photo-carriers relax by selectively coupling to only a subset of the phonon spectrum, leaving as much as 60% of the lattice heat capacity decoupled. This decoupled heat capacity is shown to be consistent with a previously undetected and partially displacive TO polar mode, indicating the DEM in LiOsO 3 . A ferroelectric metal is a peculiar state proposed by Anderson and Blunt half a century ago, but is not fully understood. Here, the authors present a time-resolved reflectivity study of LiOsO3 demonstrating evidence for decoupling of itinerant electrons and phonons in the polar transition of the material.