Excitations in the quantum paramagnetic phase of the quasi-one-dimensional Ising magnet CoNb2O6 in a transverse field: Geometric frustration and quantum renormalization effects

摘要: The quasi-one-dimensional (1D) Ising ferromagnet ${\mathrm{CoNb}}_{2}$${\mathrm{O}}_{6}$ has recently been driven via applied transverse magnetic fields through a continuous quantum phase transition from spontaneous order to paramagnet, and dramatic changes were observed in the spin dynamics, characteristic of weakly perturbed 1D criticality. We report here extensive single-crystal inelastic neutron scattering measurements excitations throughout three-dimensional (3D) Brillouin zone paramagnetic just above critical field characterize effects finite interchain couplings. In this phase, we observe that have sharp, resolution-limited line shape at low energies over most dispersion bandwidth, as expected for spin-flip quasiparticles. map full bandwidth along strongly dispersive chain direction resolve clear modulations dispersions plane normal chains, frustrated couplings an antiferromagnetic isosceles triangular lattice. can be well parametrized using linear spin-wave model includes further neighbor exchanges. is smaller than predicted by exchange values determined zero field, effect attributed renormalization beyond approximation slightly where fluctuations are still significant.