Emergence of superconductivity, valence bond order and Mott insulators in Pd[(dmit)2] based organic salts

TL;DR

This paper investigates the emergence of superconductivity, valence bond order, and Mott insulating phases in Pd[(dmit)2]-based organic salts, using theoretical modeling to explain experimental phase diagrams and predict pairing symmetry.

Contribution

It introduces a slave-rotor theoretical framework to describe competing phases and re-entrant transitions in these organic salts, capturing their complex phase behavior.

Findings

Superconductivity in EtMe3P near valence bond order boundary

Re-entrant insulator-metal-insulator transitions explained by entropy differences

Superconducting pairing symmetry identified as d ± id

Abstract

The $\EtMeP$ and $\EtMeSb$ nearly triangular organic salts are distinguished from most other Pd[(dmit)$_2$] based salts, as they display valence bond and no long range order, respectively. Under pressure, a superconducting phase is revealed in EtMe$_3$P near the boundary of valence bond order. We use slave-rotor theory with an enlarged unit cell to study competition between uniform and broken translational symmetry states, offering a theoretical framework capturing the superconducting, valence bond order, spin liquid, and metallic phases on an isotropic triangular lattice. Our finite temperature phase diagram manifests a remarkable resemblance to the phase diagram of the EtMe$_3$P salt, where the re-entrant transitions of the type insulator-metal-insulator can be explained by an entropy difference between metal and the U(1) spin liquid. We find that the superconducting pairing symmetry is $d \pm id$, and predict different temperature dependences of the specific heat between the spin liquid and metal.