High-field Magnetization Response as Evidence for Dominant Ferromagnetic Kitaev Correlations in the Alkali Iridate Na₂IrO₃

The alkali Iridate Na₂IrO₃ has received much attention, theoretically and experimentally, as a prime candidate for realizing Kitaev physics. Despite the progress made, the sign of the dominant Kitaev interaction remains an open question. The high field magnetization response is a potentially important tool for addressing this question. In this talk, I will discuss the experimentally observed magnetization response of Na₂IrO₃ for magnetic fields up to 60 Tesla, with a robust peak-dip feature at fields corresponding to the zigzag ordering ( ≈ 15K) temperature. This will be compared with the torque response obtained from numerical exact diagonalization of the well-known models used to describe Na₂IrO₃, thus constraining the effective spin models to those with a dominant ferromagnetic Kitaev and subdominant antiferromagnetic Heisenberg exchange, accompanied by smaller competing interactions. I will further discuss the nature of the spin correlation function, found to decay rapidly at high fields, akin to a quantum spin liquid state.