2D Quantum Spin-Liquid Candidate Including a Chiral Anion: κ-(BEDT-TTF)2[BR/S(salicylate)2]

Abstract

The quantum spin-liquid state was first theorized by Anderson 50 years ago and the challenge remains to realize a quantum spin-liquid material. A handful of two-dimensional molecular candidates have attracted huge attention over the past 30 years owing to their triangular lattice possessing S = 1/2 spin systems. We present a new quantum spin-liquid candidate in 2D Mott insulator κ-(BEDT-TTF)₂[B_R/S(salicylate)]₂. The structure has a double-width anion layer giving it a strong 2D character. The spiroborate anion is chiral and the salt is an inversion twin, having no inversion symmetry center and crystallizing in space group P2₁. This offers the possibility of novel behavior owing to the low symmetry not previously seen in molecular spin-liquid candidates. The peak height of the 6K anomaly of κ-(BEDT-TTF)₂[B_R/S(salicylate)₂] is 2 or 3 times larger than that of κ-(BEDT-TTF)₂Cu₂(CN)₃ and EtMe₃Sb[Pd(dmit)₂]₂. The structure presents many opportunities for crystal engineering through atom-by-atom changes to the ligands on the spiroborate anion to produce a family of materials which lie in and around the QSL region of the phase diagram for these salts. This gives the prospect of an experimental playground to deepen understanding of the QSL state. Electrical resistivity, SQUID magnetometry, band calculations, heat capacity, Infrared and Raman spectroscopy are reported for κ-(BEDT-TTF)₂[B_R/S(salicylate)₂].