Quantum integrability emerging near a quantum critical point can be manifested by exotic excitations that encode elegant algebraic structures. A well-known example is the observation of E₈ particles in CoNb₂O₆ in 2010. However, a high-resolution THz measurement in 2020 exposes additional peaks beyond E₈ description. Motivated by these, we propose a ladder model consisting of two critical Ising chains with weak interchain coupling to describe the system. Continuum limit of this model was found to be organized by another integrable field theory (IFT) with D₈⁽¹⁾ algebra. Dynamic structure factor is calculated both analytically and numerically, with good agreement obtained between the two approaches and with experimental results. Meanwhile, our analysis shows that not all particles predicted by the IFT are visible through local excitation. To resolve the discrepancy, we carry out systematic study of the Ising ladder model beyond the integrable point. Arising from the interchain coupling confinement, mesonic bound states are identified with different fermion parity and chain-exchanging symmetry. Such characterization explains the particle-selection features in the dynamical spectrum.

Inviter: Wei Li