Absence of superconductivity in the Hubbard dimer model for kappa-(BEDT-TTF)_2X

TL;DR

This study uses advanced computational methods to investigate the Hubbard dimer model for organic superconductors and finds no evidence of superconductivity, challenging theories that magnetic fluctuations drive pairing in these materials.

Contribution

The paper provides the first accurate zero-temperature DMRG calculations on the dimerized lattice, showing the absence of superconductivity in the model.

Findings

Antiferromagnetic order observed in the model.

No evidence of superconducting pairing found.

Magnetic fluctuations do not induce superconductivity in this system.

Abstract

In the most studied family of organic superconductors kappa-(BEDT-TTF)_2X, the BEDT-TTF molecules that make up the conducting planes are coupled as dimers. For some anions X, an antiferromagnetic insulator is found at low temperatures adjacent to superconductivity. With an average of one hole carrier per dimer, the BEDT-TTF band is effectively 1/2-filled. Numerous theories have suggested that fluctuations of the magnetic order can drive superconducting pairing in these models, even as direct calculations of superconducting pairing in monomer 1/2-filled band models find no superconductivity. Here we present accurate zero-temperature Density Matrix Renormalization Group (DMRG) calculations of a dimerized lattice with one hole per dimer. While we do find an antiferromagnetic state in our results, we find no evidence for superconducting pairing. This further demonstrates that magnetic fluctuations in the effective 1/2-filled band approach do not drive superconductivity in these and related materials.