Editor's suggestion article in Physical Review B

June 5, 2025

Gapped magnetic ground state in the spin-liquid candidate 𝜅−(BEDT−TTF)2⁢Ag2⁢(CN)3 suggested by magnetic spectroscopy

Gapped magnetic ground state in the spin-liquid candidate suggested by magnetic spectroscopy

Sudip Pal1, Björn Miksch1, Hans-Albrecht Krug von Nidda2, Anastasia Bauernfeind1, Marc Scheffler1, Yukihoro Yoshida3,4, Gunzi Saito3,4, Atsushi Kawamoto5, Cécile Mézière6, Narcis Avarvari6, John A. Schlueter7,8, Andrej Pustogow9, and Martin Dressel1

Abstract

The nature of the magnetic ground state of highly frustrated systems remains puzzling to this day. Here, we have performed multifrequency electron spin resonance (ESR) measurements on a putative quantum spin liquid compound 𝜅−(BEDT−TTF)2⁢Ag2⁢(CN)3, which is a rare example of 𝑆=1/2 spins on a triangular lattice. At high temperatures, the spin susceptibility exhibits a weak temperature dependence which can be described by the Heisenberg model with an antiferromagnetic exchange interaction of strength 𝐽/𝑘𝐵≈175K. At low temperatures, however, the rapid drop of the static spin susceptibility, together with monotonic decrease of the ESR linewidth, indicates that strong singlet correlations develop below a pairing energy scale 𝑇* accompanied by a spin gap. On the other hand, a weak Curie-like spin susceptibility and the angular dependence of the linewidth suggest additional contributions from impurity spins. We propose the gradual formation of spin singlets with an inhomogeneous spin gap at low temperatures.

doi.org/10.1103/PhysRevB.111.L220404

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