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

Abstract

The occurrence of antiferromagnetism (AFM) in k-(ET) 2 X 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 AFM, 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 singletpaired statecoexisting 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 k-(ET) 2 Cu 2 (CN) 3 and b 0 -EtMe 3 Sb[Pd(dmit) 2 ] 2 which we believe are PECs at low temperatures.

Charge and Lattice Fluctuations in Molecule-Based Spin Liquids

“…These triangular lattices hinder any ordering pattern of the spin arrangements being made when the spins are affected by antiferromagnetic interactions, which leads to geometrical frustration. It is within this context that some two-dimensional (2D) molecular solids have attracted a lot of interest, as their spin systems possess triangular lattices with S  = 1/2 3–13 ; examples of such solids include β ′-EtMe 3 Sb[Pd(dmit) 2 ] 2 [dmit = 1,3-dithiole-2-thione-4,5-dithiolate], κ -(ET) 2 M 2 (CN) 3 [ET = bis(ethylenedithio)tetrathiafulvalene, M = Cu and Ag] and κ -H 3 (Cat-EDT-TTF) 2 [ = catechol-fused ethylenedithiotetrathiafulvalene] 14–23 . The triangular lattices of β ′-EtMe 3 Sb[Pd(dmit) 2 ] 2 are comprised of a pair of independent monomers (Fig.…”

Is there a common theme behind the correlated‐electron superconductivity in organic charge‐transfer solids, cobaltates, spinels, and fullerides?

“…The key step is the realization that antiferromagnetism in the semiconducting state does not necessarily mean that the electronic structure of the superconductor is derived from the same configuration. Bandwidth-driven transition to a different state that is more appropriately described as 1/4-filled can occur in the superconducting state [14]. This has been explicitly shown in the context of the CTS.…”

“…We have proposed that with further increase in frustration the PEC gives way to a superconducting paired-electron liquid [14]. The proposed theory of SC is essentially the same as that of Schafroth, within which electron-pairs form mobile molecules (charged bosons) [1].…”

“…The limitation of SC to r ¼ 0.5 acquires additional significance when taken together with: (a) absence of SC in the r ¼ 1 triangular lattice Hubbard Hamiltonian [13], (b) the propensity at r ¼ 0.5 to form the paired-electron crystal (PEC), in which spin-singlet pairs are separated by pairs of vacant sites, in both 1D and the moderately frustrated anisotropic triangular lattice [14]. We have proposed that with further increase in frustration the PEC gives way to a superconducting paired-electron liquid [14].…”

Vibrational and Electronic Structure, Electron-Electron and Electron-Phonon Interactions in Organic Conductors Investigated by Optical Spectroscopy

“…The family of two-dimensional ET salts with half-filled band are especially interesting for the charge disproportionation phenomena and has been extensively investigated [64][65][66][67][68][69][70][71], with the special focus on the κ-phase salts [72][73][74][75][76][77][78][79]. However, such phenomenon in such group of salts The phase transition at 150 K induces considerable modifications in electronic structures.…”