Abstract

Triangular lattices are uncomfortable stages for interacting electrons, however, which bring about emergent states. In half-filled band systems, antiferromagnetically interacting spins are strongly frustrated and may exhibit a quantum spin liquid (QSL). In quarter-filled band systems, Coulomb interacting electrons fail to form a Wigner crystal on a triangular lattice but may freeze into a charge glass (CG) state, which even may quantum　melt. The organic κ-ET salts and θ-ET salts are good model systems for the former and latter subjects, respectively. I present our updated results on these two issues.

For the issue of QSL, I summarize the present experimental status on the QSL candidate, κ-(ET)2Cu2(CN)3, and also show non-Fermi liquidity, quantum criticality, BEC-like superconductivity in the doped QSL candidate, κ-(ET)4Hg2.89Br8. For the issue of CG, I show quantum-classical dual properties of glasses exhibited by a series of θ-ET2X.