Fragility of the Quantum Spin Liquid State: The Case of Organic Charge Transfer Salts*

The geometrically frustrated organic charge transfer salts have proven to host a number of good candidates for quantum spin liquids (QSL). Although these compounds have been the subject of extensive experimental studies in the past, the theoretical explanation of their properties is in many cases still an open issue. One interaction that has been rarely considered to influence the QSL systems is spin-orbit coupling, due to the light C, S, H atoms in organics. We previously suggested (1) that an effective staggered field, caused by Dzyaloshinskii-Moriya interaction, can induce a critical response under magnetic field, if the QSL materials are close to magnetic order. Here, we predict how the critical response is reflected in a range of experiments, such as μSR, ESR, NMR and magnetic torque. We compare the predictions to recent experimental results on a number of candidate materials (2-4). The position of each material in the phase diagram determines hereby the critical response and the fragility of the QSL state with respect to field induced order (5).

(1) S. M. Winter et al., PRB 95, 060404(R) (2017)
(2) F. Pratt et al., Nature 471, 612 (2011)
(3) T. Isono et al., Nat. Commun. 7, 13494 (2016)
(4) T. Isono et al., PRL 112, 177201 (2014)
(5) K. Riedl et al., in preparation