Orthorhombic fulleride (CH3NH2)K3C60 close to Mott-Hubbard instability: Ab initio study

Abstract

We study the electronic structure and magnetic interactions in methylamine-intercalated orthorhombic alkali-doped fullerene (CH3NH2)K3C60 within the density functional theory. As in the simpler ammonia intercalated compound (NH3)K3C60, the orthorhombic crystal-field anisotropy Δlifts the t1u triple degeneracy at the Γpoint and drives the system deep into the Mott-insulating phase. However, the computed Δand conduction electron bandwidth W cannot alone account for the abnormally low experimental Néel temperature, T_N = 11 K of the methylamine compound, compared to the much higher value T_N = 40 K of the ammonia one. Significant interactions between CH3NH2 and C60^{3-} are responsible for the stabilization of particular pseudo-Jahn-Teller fullerene-cage distortions and the ensuing low-spin S = 1/2 state. These interactions also seem to affect the magnetic properties, as interfullerene exchange interactions depend on the relative orientation of pseudo-Jahn-Teller distortions of neighboring C60^{3-} molecules. For the ferro-orientational order of CH3NH2-K^+ groups we find an apparent reduced dimensionality in magnetic exchange interactions, which may explain the suppressed Néel temperature. The disorder in exchange interactions caused by orientational disorder of CH3NH2-K^+ groups could further contribute to this suppression.

8 pages, 5 figures, 1 table

References in corpus (4)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Modeling the Unconventional Superconducting Properties of Expanded A${}_3$C${}_{60}$ Fullerides
• Ab initio derivation of electronic low-energy models for C60 and aromatic compounds
• NMR study of the Mott transitions to superconductivity in the two Cs_3C_60 phases

Cited by in corpus (5)

• Exotic s-wave superconductivity in alkali-doped fullerides
• Dynamical Jahn--Teller effect and antiferromagnetism in Cs${}_3$C${}_{60}$
• Dynamical Jahn--Teller instability in metallic fullerides
• Sliding states of a soft-colloid cluster crystal: Cluster versus single-particle hopping
• Survival of the metallic state in a single-hole multiband $p$-orbital molecular system