Beyond the quantum spin liquid concept in frustrated two dimensional organic superconductors

TL;DR

This paper challenges the traditional quantum spin liquid concept in frustrated organic superconductors, proposing that a Paired Electron Crystal state better explains their low-temperature behavior.

Contribution

It introduces the Paired Electron Crystal as a new state in highly frustrated 1/4-filled lattices, expanding understanding beyond quantum spin liquids.

Findings

Identification of regions with AFM, PEC, and Wigner-crystal phases

Demonstration that PEC coexists with charge ordering in the model

Arguing that certain materials are better described as PECs at low temperatures

Abstract

The occurrence of antiferromagnetism in kappa-(ET)_2X can be understood within an effective 1/2-filled band with dimers of ET molecules containing one hole each. We argue that while this effective model can describe the presence of antiferromagnetism, a complete description for these materials requires the correct carrier density of one-half per molecule. For dimerized and strongly frustrated 1/4-filled lattices we show that a singlet-paired state coexisting with charge ordering occurs that we have termed the Paired Electron Crystal (PEC). Here we investigate the 1/4-filled model on a dimerized lattice, showing regions where AFM, PEC, and the Wigner-crystal occur. We point out the need to go beyond quantum spin liquid concepts for highly frustrated materials such as kappa-(ET)_2Cu_2(CN)_3 and beta'-EtMe_3Sb[Pd(dmit)_2]_2 which we believe are PECs at low temperatures.