Single-ion properties of quasi-1D transverse Ising-critical CoNb₂O₆

The transverse-field Ising model (TFIM) is the most theoretically tractable model that displays a quantum phase transition. CoNb₂O₆ is one of the few known real materials to exhibit a quantum critical point in the presence of an applied transverse field. However, despite having long been modeled as a truly Ising-like system, recent theoretical results [1] suggest that the critical behavior observed in CoNb₂O₆ is due not to the breaking of a global Ising symmetry, but to the breaking of a glide symmetry which is a consequence of its 3D space group Pbcn (60). Additionally, THz spectroscopy measurements have indicated that the magnetism in CoNb₂O₆ possibly approximates the "twisted" Kitaev chain model [2]. In both cases the model maps onto the TFIM through a unitary transformation, keeping the observed critical behavior within the same Ising universality class. We present the results of both inelastic neutron scattering measurements and electron paramagnetic resonance spectroscopy on CoNb₂O₆, which explores the single-ion anisotropy present in the local environments of the Co²⁺ ions in an effort to shed light on these recent developments.

[1] M. Fava et al. arXiv: 2004.04169 (2020).
[2] C.M. Morris et al. arXiv: 2009.14189 (2020).