Excitations of quantum Ising chain CoNb2O6 in low transverse field: quantitative description of bound states stabilized by off-diagonal exchange and applied field

Abstract

We present experimental and theoretical evidence of novel bound state formation in the low transverse field ordered phase of the quasi-one-dimensional Ising-like material CoNb${}_2$O${}_6$. High resolution single crystal inelastic neutron scattering measurements observe that small transverse fields lead to a breakup of the spectrum into three parts, each evolving very differently upon increasing field. This can be naturally understood starting from the excitations of the ordered phase of the transverse field Ising model, domain wall quasiparticles (solitons). Here, the transverse field and a staggered off-diagonal exchange create one-soliton hopping terms with opposite signs. We show that this leads to a rich spectrum and a special field, when the strengths of the off-diagonal exchange and transverse field match, at which solitons become localized; the highest field investigated is very close to this special regime. We solve this case analytically and find three two-soliton continua, along with three novel bound states. Perturbing away from this novel localized limit, we find very good qualitative agreement with the experimental data. We also present calculations using exact diagonalization of a recently refined Hamiltonian model for CoNb${}_2$O${}_6$ and using diagonalization of the two-soliton subspace, both of which provide a quantitative agreement with the observed spectrum. The theoretical models qualitatively and quantitatively capture a variety of non-trivial features in the observed spectrum, providing insight into the underlying physics of bound state formation.

arXiv comment17 pages, 5 figures. Accepted version after comments from referees

References in corpus (8)

• Quantum criticality in an Ising chain: experimental evidence for emergent E8 symmetry
• Evolution of Quantum Fluctuations Near the Quantum Critical Point of the Transverse Field Ising Chain System CoNb${}_2$O${}_6$
• A hierarchy of bound states in the 1D ferromagnetic Ising chain CoNb${}_2$O${}_6$ investigated by high resolution time-domain terahertz spectroscopy
• Heat capacity anomaly at the quantum critical point of the Transverse Ising Magnet CoNb_2O_6
• Duality and domain wall dynamics in a twisted Kitaev chain
• Glide symmetry breaking and Ising criticality in the quasi-1D magnet CoNb${}_2$O${}_6$
• Experimental Observation of Quantum Many-Body Excitations of $E_8$ Symmetry in the Ising Chain Ferromagnet CoNb${}_2$O${}_6$
• Tuning the confinement potential between spinons in the Ising chain CoNb2O6 using longitudinal fields and quantitative determination of the microscopic Hamiltonian

Cited by in corpus (6)

• Tuning the confinement potential between spinons in the Ising chain CoNb2O6 using longitudinal fields and quantitative determination of the microscopic Hamiltonian
• Magnon interactions in the quantum paramagnetic phase of CoNb${}_2$O${}_6$
• Transforming from Kitaev to Disguised Ising Chain: Application to CoNb${}_2$O${}_6$
• Cobalt-Based Pyroxenes: A New Playground for Kitaev Physics and Ising Model Realization
• Signatures of Domain-Wall Confinement in Raman Spectroscopy of Ising Spin Chains
• Emergent $D_8^{(1)}$ spectrum and topological soliton excitation in CoNb${}_2$O${}_6$