Saturday, April 3, 2010

Frustration controlled metal-insulator transition

The Mott insulating phase occurs at half filling and when the on-site Coulomb repulsion U is much larger than the hopping energy t and the associated band width. A transition to a metallic phase occurs either by doping away from half filling [FC-MIT= filling controlled metal-insulator transition] or by decreasing the ratio U/t [BC-MIT bandwidth controlled metal-insulator transition]. In the cuprates FC-MIT occurs whereas in the organic charge transfer salts such as (BEDT-TTF)2X one might argue that the BC-MIT occurs.
On the other hand, perhaps one should consider a third co-ordinate, the frustration, in addition to the filling and band width. This would lead to the notion of an FrC-MIT, a frustration controlled transition.
In the Hubbard model on the anisotropic triangular lattice at half-filling for fixed U/t increasing t'/t can drive an insulator to metal transition, as shown in the Figure below taken from

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