Negative Magnetoresistance near the Mott Metal–Insulator Transition in the Quantum Spin Liquid Candidate κ-(BEDT-TTF)₂Cu₂(CN)₃

We investigate the in-plane magnetoresistance of the quantum spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3 near the metal–insulator phase boundary by fine-tuning the uniaxial strain of a thin single crystal. Negative magnetoresistance up to −40% is observed, implying that the insulating state below ∼6 K has lower intrinsic magnetism than the metallic state. The result is consistent with the recent remarks on the nonmagnetic transition to a valence-bond solid ground state.