Comparative study of organic metals and high-T$_c$ cuprates

TL;DR

This paper compares the electronic properties and correlations in organic metals and high-temperature cuprates, highlighting similarities and differences in their models, interactions, and charge transfer phenomena.

Contribution

It provides a detailed comparative analysis of the band structures, interactions, and collective modes in organics and cuprates, emphasizing the role of charge transfer and lattice coupling.

Findings

Similar coherent SDW and charge-transfer correlations in both materials.

Incommensurate SDW and charge transfer modes are enhanced with doping.

Nematic stripe order is associated with static incommensurate charge transfer in cuprates.

Abstract

The Bechgaard salts and the high T$_c$ cuprates are described by two and three band models, respectively, with the lowest band (nearly) half filled. In organics the interactions are small, while in cuprates the repulsion $U_d$ on the Cu site is the largest energy. The Mott AF state is stable in undoped materials in both cases. In the metallic phase of cuprates the $U_d\to\infty$ limit produces a moderate effective repulsion. The theories of the coherent SDW and charge-transfer correlations in the metallic phases of organics and cuprates are thus similar. In (undoped) organics those correlations are associated with commensurate $2k_F$ SDW and $4k_F$ bond or site modes. The corresponding modes in metallic cuprates are the incommensurate SDW and in particular O$_x$/O$_y$ quadrupolar charge transfer with wave vector $2q_{SDW}=q_0+G$. They are enhanced for dopings $x>0$, which bring the Fermi level close to the van Hove singularity. Strong coupling to the lattice associates the static incommensurate O$_x$/O$_y$ charge transfer with collinear "nematic" stripes. In contrast to organics, the coherent correlations in cuprates compete with local $d_{10}\leftrightarrow d_9$ quantum charge-transfer disorder.