Fate of frustrated electrons in solids
鹿野田 一司 教授
Coulomb interaction among electrons has huge impacts on their behaviour in solids. Two major effects, localization of charges and enhancement of spin correlation, lead to diverse emergent phenomena. In particular, on triangular lattices, electrons may exhibit non-trivial spin and charge states. As depicted in the left figure, electron spins with antiparallel interactions between neighbours cannot find a preferential spin configuration. In another case, in which that electron density is 0.5 per site (right figure), electrons cannot form a regular lattice. The geometrical frustration prohibits ordering in spin and charge degrees of freedom. Then, what is their ground state? For exploring this issue, molecular materials are superior model systems in that the lattice geometry is controllable through chemical substitution and pressure. In this seminar, I present experimental indications of the emergence of exotic electronic states on quasi-triangular lattice; a quantum spin liquid and a charge glass. I also touch the issues of Mott metal-insulator transition, unconventional superconductivity and massless Dirac electrons that show up in the neighborhood.