Buckling induced Zener polaron instability in half-doped manganites

TL;DR

This paper investigates how oxygen buckling in half-doped manganites leads to a Zener polaron instability, resulting in a multiferroic ground state with dimerized spins, orbitals, and lattice structures.

Contribution

It reveals the steric role of oxygen buckling in inducing Zener polaron formation and multiferroicity in manganites, a novel insight into their electronic and structural behavior.

Findings

Oxygen buckling causes MnO6 tilting without changing Mn-Mn bonds.

Buckling drives the system towards dimerization instability.

Beyond a critical buckling, a multiferroic Zener polaron ground state forms.

Abstract

By calculating the electronic, orbital, magnetic and lattice structure of half-doped manganites we establish the central role of oxygen buckling caused by the tilting of the MnO$_6$ octahedra -- in essence a steric effect. The buckling itself does not change the Mn-Mn bonds. Instead it drives the system towards an instability where these bonds can dimerize. In presence of electron-electron interactions, this instability can fully develop and beyond a critical buckling a Zener polaron groundstate with dimerized spins, lattice and orbitals forms spontaneously, resulting in a multiferroic state.