Magnetic anisotropy of the alkali iridate Na2IrO3 at high magnetic fields:Evidence for strong ferromagnetic Kitaev correlations

摘要: The magnetic-field response of the Mott-insulating honeycomb iridate ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ is investigated using torque magnetometry measurements in magnetic fields up to 60 T. A peak-dip structure observed at corresponding an energy scale close zigzag ordering ($\ensuremath{\approx}15\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) temperature. Using exact diagonalization calculations, we show that such a distinctive signature constrains effective spin models for these classes Kitaev materials ones with dominant ferromagnetic interactions, while alternative antiferromagnetic interactions are excluded. We further that, high fields, long range correlation functions decay rapidly, pointing transition long-sought-after field-induced quantum liquid beyond structure, suggesting this be common feature family systems. systems thus revealed excellent candidates liquids, similar physics having been suggested another system $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$.