セミナー情報

Quantum spin-liquids are exotic states of matter where interacting spins continue to fluctuate down to absolute zero temperature due to strong quantum fluctuations. In particular, two-dimensional spin-liquids in frustrated quantum magnets have been long sought after since Anderson’s proposals for a resonating valence bond phase and its possible link to the high-T_c cuprate superconductivity. Only recently, a few candidate materials have emerged. For example, Herbertsmithite, ZnCu₃(OH)₆Cl₂, is a unique representative of the quantum (S=1/2) kagome antiferromagnet, which displays a gapless spin-liquid behaviors down to 50 mK, 1/4000th of its exchange energy. In this talk, I will present our recent NMR results which uncover an instability of the spin-liquid phase of Herbertsmithite toward a spin-solid phase induced by an applied magnetic field. We find the zero-temperature phase transition appears at a finite magnetic field much smaller than the exchange energy scale. I will discuss the implication of this quantum critical point in light of the recent theoretical proposals for the gapless or gapped spin-liquid ground-state of the quantum kagome Heisenberg antiferromagnet as well as the quantum phase transition driven by perturbative Dzyaloshinskii-Moriya interaction.