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
- 1Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
- 2Experimental Physics V, Center for Electronic Correlations and Magnetism, Universität Augsburg, Universitätsstraße 1, 86159 Augsburg, Germany
- 3Faculty of Agriculture, Meijo University, Nagoya 468-8502, Japan
- 4Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- 5Department of Science, Hokkaido University, Sapporo 060-0810, Japan
- 6Univ Angers, CNRS, MOLTECH-Anjou, SFR MATRIX, 49000 Angers, France
- 7Material Science Division, Argonne National Laboratory, Argonne, Illinois 60439-4831, USA
- 8National Science Foundation, Alexandria, Virginia 22314, USA
- 9Institute of Solid State Physics, TU Wien, 1040 Vienna, Austria
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)2Ag2(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.