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<p>This study reports the observation of phonon-drag thermopower polarity reversal in Ba-doped KTaO<sub>3</sub> thin films, mediated by electron-phonon Umklapp scattering. Epitaxial films with distinct carrier concentrations (3.3 × 10<sup>18 </sup>cm<sup>-3</sup>, 4.9 × 10<sup>19 </sup>cm<sup>-3</sup>, and 3.7 × 10<sup>20 </sup>cm<sup>-3</sup>) were grown via molecular-beam epitaxy. In the heavily doped sample, where the Fermi surface spans 80% of the Brillouin zone in some directions, the Umklapp condition is satisfied, reversing electron momentum. This manifests as a sign-reversal in the thermopower around 80 K upon cooling despite the sample having only n-type carriers. On the other hand, the lightly doped samples (3.3 × 10<sup>18</sup> and 4.9 × 10<sup>19 </sup>cm<sup>-3</sup>) exhibit only a negative thermopower down to 2 K. These results advance the understanding of Umklapp electron-phonon-drag in oxides and highlight KTaO<sub>3</sub>’s potential for engineering unconventional thermoelectric materials.</p>

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Large phonon-drag thermopower polarity reversal in Ba-doped KTaO3

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月28日

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  • Mohamed Nawwar,
  • Samuel Poage,
  • Tobias Schwaigert,
  • Maria N. Gastiasoro,
  • Salva Salmani-Rezaie,
  • Darrell G. Schlom,
  • Kaveh Ahadi,
  • Brandi L. Wooten,
  • Joseph P. Heremans

摘要

This study reports the observation of phonon-drag thermopower polarity reversal in Ba-doped KTaO3 thin films, mediated by electron-phonon Umklapp scattering. Epitaxial films with distinct carrier concentrations (3.3 × 1018 cm-3, 4.9 × 1019 cm-3, and 3.7 × 1020 cm-3) were grown via molecular-beam epitaxy. In the heavily doped sample, where the Fermi surface spans 80% of the Brillouin zone in some directions, the Umklapp condition is satisfied, reversing electron momentum. This manifests as a sign-reversal in the thermopower around 80 K upon cooling despite the sample having only n-type carriers. On the other hand, the lightly doped samples (3.3 × 1018 and 4.9 × 1019 cm-3) exhibit only a negative thermopower down to 2 K. These results advance the understanding of Umklapp electron-phonon-drag in oxides and highlight KTaO3’s potential for engineering unconventional thermoelectric materials.