Static magnetic order with strong quantum fluctuations in spin-1/2 honeycomb magnet Na2Co2TeO6

Abstract

Kitaev interactions, arising from the interplay of frustration and bond anisotropy, can lead to strong quantum fluctuations and, in an ideal case, to a quantum-spin-liquid state. However, in many nonideal materials, spurious non-Kitaev interactions typically promote a zigzag antiferromagnetic order in the d-orbital transition-metal compounds. Here, by combining neutron scattering with muon-spin rotation and relaxation techniques, we provide mechanism insights into the exotic properties of Na2Co2TeO6, a candidate material of the Kitaev model. Below TN, the zero-field muon-spin relaxation rate becomes almost constant (~0.45 μs−1). We attribute this temperature-independent relaxation rate to the strong quantum fluctuations, as well as to the frustrated Kitaev interactions. As the magnetic field increases, neutron scattering data indicate a broader spin-wave excitation at the K-point. Therefore, quantum fluctuations seem not only robust but are even enhanced by the applied magnetic field. Our findings provide valuable hints for understanding the onset of the quantum-spin-liquid state in Kitaev materials. Na2Co2TeO6 is a candidate Kitaev spin-liquid, but the nature of its ground state remains controversial, as spurious non-Kitaev exchange interactions promote magnetic ordering. Here, neutron scattering and muon-spin rotation experiments indicate the presence of strong quantum fluctuations in the ground state, giving rise to a multi-domain zigzag antiferromagnetic order.