Abstract: We show [1] that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures [2]. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of super-cooled liquids around the glass transition. Our results show remarkable similarity with the recent observations [3,4] of charge-glass behavior in ultra-clean triangular organic materials of the θ-(BEDT-TTF) family.

1.S. Mahmoudian, L. Rademaker, A. Ralko, S. Fratini, V. Dobrosavljević, submitted to Phys. Rev. Lett., preprint arXiv:1412.4441.
2.J. Schmalian and P. G. Wolynes, Phys. Rev. Lett. 85, 836 (2000).
3.F. Kagawa, T. Sato, K. Miyagawa, K. Kanoda, Y. Tokura, K. Kobayashi, R. Kumai, and Y. Murakami, Nat. Phys. 9, 422 (2013).
4.H. Oike, F. Kagawa, N. Ogawa, A. Ueda, H. Mori, M. Kawasaki, and Y. Tokura, Phys. Rev. B 91, 041101 (2015).