Electron-phonon coupling and superconductivity in the doped topological-crystalline insulator (Pb$_{0.5}$Sn$_{0.5}$)$_{1-x}$In$_x$Te
Phys. Rev. B 102, 104511 (2020) We present a neutron scattering study of phonons in single crystals of (Pb$_{0.5}$Sn$_{0.5}$)$_{1-x}$In$_x$Te with $x=0$ (metallic, but nonsuperconducting) and $x=0.2$ (nonmetallic normal state, but superconducting). We map the phonon dispersions (more completely for...
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Main Authors | , , , , , , , , , , , , , , |
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Format | Journal Article |
Language | English |
Published |
06.07.2020
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Subjects | |
Online Access | Get full text |
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Summary: | Phys. Rev. B 102, 104511 (2020) We present a neutron scattering study of phonons in single crystals of
(Pb$_{0.5}$Sn$_{0.5}$)$_{1-x}$In$_x$Te with $x=0$ (metallic, but
nonsuperconducting) and $x=0.2$ (nonmetallic normal state, but
superconducting). We map the phonon dispersions (more completely for $x=0$) and
find general consistency with theoretical calculations, except for the
transverse and longitudinal optical (TO and LO) modes at the Brillouin zone
center. At low temperature, both modes are strongly damped but sit at a finite
energy ($\sim4$ meV in both samples), shifting to higher energy at room
temperature. These modes are soft due to a proximate structural instability
driven by the sensitivity of Pb-Te and Sn-Te $p$-orbital hybridization to
off-center displacements of the metal atoms. The impact of the soft optical
modes on the low-energy acoustic modes is inferred from the low thermal
conductivity, especially at low temperature. Given that the strongest
electron-phonon coupling is predicted for the LO mode, which should be similar
for both studied compositions, it is intriguing that only the In-doped crystal
is superconducting. In addition, we observe elastic diffuse (Huang) scattering
that is qualitatively explained by the difference in Pb-Te and Sn-Te bond
lengths within the lattice of randomly distributed Pb and Sn sites. We also
confirm the presence of anomalous diffuse low-energy atomic vibrations that we
speculatively attribute to local fluctuations of individual Pb atoms between
off-center sites. |
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DOI: | 10.48550/arxiv.2007.03091 |