Design and Preparation of a Quantum Spin Liquid Candidate κ-(ET)2Ag2(CN)3 Having a Nearby Superconductivity

Abstract

Abstract Similar to the first quantum spin liquid (QSL) candidate, κ-(ET)2Cu2(CN)3 (1), newly prepared κ-(ET)2Ag2(CN)3 (2) is a dimer Mott insulator with a QSL ground state at ambient pressure and exhibits metallic and superconducting states next to the QSL state under pressure, where ET is bis(ethylenedithio)tetrathiafulvalene. The packing of the ET dimer, which corresponds to a single spin site (S = 1/2), in 2 is similar to that in 1. Salt 2 afforded a two-dimensional equilateral triangular spin lattice having strong geometrical spin frustration (t′/t = 0.967) similar to 1 (t′/t = 1.09), where t and t′ are the interdimer transfer interactions. The geometric relationship between the spin site and the opening in the anion layer in 2 is considerably different from that in 1, resulting in more dispersed packing of ET dimers, narrower bandwidth W, and larger on-site Coulomb repulsion energy U for 2 than 1. As a consequence, 2 has a higher electron correlation U/W, more robust QSL state for wider pressure range and is allocated far away from the itinerant region compared to those of 1. The narrower bandwidth is consistent with a higher superconducting critical temperature for 2 than 1 under pressure.