Spin excitations of a proximate Kitaev quantum spin liquid realized in Cu₂IrO₃

2022/03/08 by Sean K. Takahashi, Jiaming Wang, Alexandre Arsenault +4 · 1 citation
Physics and Astronomy · #cond-mat.str-el

paper · pdf · doi:10.1103/physrevx.9.031047

published as Phys. Rev. X 9, 031047 (2019) · 18 figs

arxiv created 2022/03/08 · arxiv updated 2022/03/09

Abstract

Magnetic moments arranged at the corners of a honeycomb lattice are predicted to form a novel state of matter, Kitaev quantum spin liquid, under the influence of frustration effects between bond-dependent Ising interactions. Some layered honeycomb iridates and related materials, such as Na₂IrO₃ and α-RuCl₃, are proximate to Kitaev quantum spin liquid, but bosonic spin-wave excitations associated with undesirable antiferromagnetic long-range order mask the inherent properties of Kitaev Hamiltonian. Here, we use ⁶³Cu nuclear quadrupole resonance to uncover the low energy spin excitations in the nearly ideal honeycomb lattice of effective spin S = 1/2 at the Ir⁴⁺ sites in Cu₂IrO₃. We demonstrate that, unlike Na₂IrO₃, Ir spin fluctuations exhibit no evidence for critical slowing down toward magnetic long range order in zero external magnetic field. Moreover, the low energy spin excitation spectrum is dominated by a mode that has a large excitation gap comparable to the Ising interactions, a signature expected for Majorana fermions of Kitaev quantum spin liquid.

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