Spin versus lattice polaron: Prediction for electron-doped CaMnO3

Yiing-Rei Chen*, P. B. Allen

*此作品的通信作者

研究成果: 雜誌貢獻期刊論文同行評審

24 引文 斯高帕斯(Scopus)

摘要

CaMnO3 is a simple bipartite antiferromagnet (AF) that can be continuously electron doped up to LaMnO3. Electrons enter the doubly degenerate Eg subshell with spins aligned to the S = 3/2 core of Mn4+(T2g3↑. We take the Hubbard and Hund energies to be effectively infinite. Our model Hamiltonian has two Egorbitals per Mn atom, nearest-neighbor hopping, nearest neighbor exchange coupling of the S = 3/2 cores, and electron-phonon coupling of Mn orbitals to adjacent oxygen atoms. We solve this model for light doping. Electrons are confined in local ferromagnetic (FM) regions (spin polarons) where there proceeds an interesting competition between spin polarization (spin polarons), which enlarges the polaron, and lattice polarization (Jahn-Teller polarons), which makes it smaller. A symmetric seven-atom ferromagnetic cluster (Mn727+) is the stable result, with a net spin S = 2 relative to the undoped AF. The distorted oxygen positions around the electron are predicted. The possibility that two electrons will form a bipolaron has been considered. A fairly modest Coulomb repulsion Uc=0.98|t| (where t≈-0.75 eV) will destroy any simple bipolaron. Therefore we do not expect phase separation to occur. The model predicts a critical doping x∼0.045 where the polaronic insulator becomes unstable relative to a FM metal.

原文英語
文章編號064401
頁(從 - 到)644011-644018
頁數8
期刊Physical Review B - Condensed Matter and Materials Physics
64
發行號6
出版狀態已發佈 - 2001 八月 1

ASJC Scopus subject areas

  • 電子、光磁材料
  • 凝聚態物理學

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