Mott Transition and Phase Diagram of $κ$-(BEDT-TTF)2Cu(NCS)2 Studied by Two-Dimensional Model Derived from Ab initio Method

Details Mott Transition and Phase Diagram of $κ$-(BEDT-TTF)2Cu(NCS)2 Studied by Two-Dimensional Model Derived from Ab initio Method Mott Transition and Phase Diagram of $κ$-(BEDT-TTF)2Cu(NCS)2 Studied by Two-Dimensional Model Derived from Ab initio Method

2011-10-28

arxiv.org/abs/1110.6299v2

J. Phys. Soc. Jpn. 81, 034701(1-12) (2012)

Physics

Condensed Matter

Strongly Correlated Electrons

15 pages, 11 figures (minor revision, to appear in JPSJ)

Scientific paper

10.1143/JPSJ.81.034701

We present an ab initio analysis for the ground-state properties of a correlated organic compound $\kappa$-(BEDT-TTF)2Cu(NCS)2. First, we derive an effective two-dimensional low-energy model from first principles, having short-ranged transfers and short-ranged Coulomb and exchange interactions. Then, we perform many-variable variational Monte Carlo calculations for this model and draw a ground-state phase diagram as functions of scaling parameters for the onsite and off-site interactions. The phase diagram consists of three phases; a paramagnetic metallic phase, an antiferromagnetic (Mott) insulating phase, and a charge-ordered insulating phase. In the phase diagram, the parameters for the real compound are close to the first-order Mott transition, being consistent with experiments. We show that the off-site Coulomb and exchange interactions affect the phase boundary; (i) they appreciably stabilize the metallic state against the Mott insulating phase and (ii) enhance charge fluctuations in a wide parameter region in the metallic phase. We observe arc-like structure in Fermi surface around the region where the charge fluctuations are enhanced. Possible relevance of the charge fluctuations to the experimentally observed dielectric anomaly in the $\kappa$-BEDT-TTF family compounds is also pointed out.

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