Novel Orientational Ordering and Reentrant Metallicity in KxC60 Monolayers for 3 <= x <= 5

• Main Authors: Wang, Yayu, Yamachika, R, Wachowiak, A, Grobis, M, Khoo, K. H, Lee, D. H, Louie, Steven G, Crommie, M. F
• Format: Journal Article
• Language: English
• Published: 04-12-2007
• Subjects: Physics - Materials Science; Physics - Strongly Correlated Electrons
• DOI: 10.48550/arxiv.0712.0421

Phys. Rev. Lett. 99, 086402 (2007) We have performed local STM studies on potassium-doped C60 (KxC60) monolayers
over a wide regime of the phase diagram. As K content increases from x = 3 to
5, KxC60 monolayers undergo metal-insulator-metal reentrant phase transitions
and exhibit a variety of novel orientational orderings. The most striking new
structure has a pinwheel-like 7-molecule unit cell in insulating K4+dC60. We
propose that the driving mechanism for the orientational ordering in KxC60 is
the lowering of electron kinetic energy through maximization of the overlap of
neighboring molecular orbitals over the entire doping range x = 3 to 5. In the
insulating and metallic phases this gives rise to orbital versions of the
superexchange and double-exchange interactions respectively.