High Field NMR Investigation of Kitaev Spin Liquid Candidate Cu2IrO3

Abstract

The search for quantum spin liquids (QSLs) introduces some of the most challenging and interesting problems in contemporary physics. The recently discovered iridate Cu2IrO3,which contains a honeycomb lattice of Ir4+ions with effective spin 1/2 coupled by frustrated Ising interactions, presents itself as a promising candidate for a Kitaev QSL. In this study, we use nuclear magnetic resonance (NMR), a spectroscopic technique based on the energy levels of nuclear spin states, to probe the intrinsic spin excitations of Cu2IrO3. By measuring the NMR frequency shift of 63Cu from 4.2 K to 298 K,we demonstrate that its spin susceptibility χ spin behaves nearly identically to its parent compound Na2IrO3, without showing evidence of magnetic ordering at low temperatures. We showed that the upturn of bulk susceptibility χ below T=50 K is due to the contribution of defect spins. The hyperfine coupling constant Ahf between Cu and Ir4+was also estimated by comparing the Knight shift 63K to χ