Importance of randomness in a quantum spin liquid candidate revealed by artificial distortion of triangular lattices

Orateur : Yohei SAITO (1. Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany)

Quantum spin liquid (QSL) candidates which do not show magnetic ordering even though magnetic interactio n is strong have long had questions about the mechanism to realize the QSL states in solid state physics. Could it be due to ideal geometrical frustration of spins on triangular lattices ? Or could it be due to randomness ? If the absence of magnetic ordering is caused by the geometrical frustration, the magnetic property should change by suppressing the geometrical frustration. To clarify that, I give a distinct way to investigate spin liquid candidate materials by artificial distortion of triangular lattices. I artificially distorted triangular lattices of a QSL candidate of an organic conductor kappa-(ET)2Cu2(CN)3 by impurity donor molecular substitution. The substitution modifies exchange interactions among the substituted molecules. As a result, geometrical frustration is suppressed locally. I performed 13C NMR, electric conductivity, and static susceptibility measurements. Comparing results of non-substituted and substituted samples, I found that their magnetic fluctuation was t he same even at temperatures two orders of magnitude less than the exchange interaction as opposed to the remarkable impurity substitution effect of the conductivity. Thus, I demonstrated that the electronic state of the (CN)3 salt is already disordered even in the non-substituted sample, and that not only the ideal geometrical frustration but also the disorder effect should be considered. The method used in this study can be applied for other QSL candidates and it will help to understand the mechanism of quantum states.

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