Abstract
We study the dynamics of the quasi-one-dimensional Ising-Heisenberg antiferromagnet ${\mathrm{BaCo}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ under a transverse magnetic field. Combining inelastic neutron scattering experiments and theoretical analyses by field theories and numerical simulations, we mainly elucidate the structure of the spin excitation spectrum in the high-field phase, appearing above the quantum phase transition point ${\ensuremath{\mu}}_{0}{H}_{c}\ensuremath{\approx}10\phantom{\rule{0.28em}{0ex}}\mathrm{T}$. We find that it is characterized by collective solitonic excitations superimposed on a continuum. These solitons are strongly bound in pairs due to the effective staggered field induced by the nondiagonal $g$ tensor of the compound and are topologically different from the fractionalized spinons in the weak-field region. The dynamical susceptibility numerically calculated with the infinite time-evolving block decimation method shows an excellent agreement with the measured spectra, which enables us to identify the dispersion branches with elementary excitations. The lowest-energy dispersion has an incommensurate nature and has a local minimum at an irrational wave number due to the applied transverse field.
Highlights
Intensive efforts are currently being made to investigate materials exhibiting prominent quantum effects
These solitons are strongly bound in pairs due to the effective staggered field induced by the nondiagonal g tensor of the compound and are topologically different from the fractionalized spinons in the weak-field region
We present the results of the Inelastic neutron scattering (INS) measurements and elucidate the dynamics of BaCo2V2O8 under the large transverse magnetic field by comparing the experimental data with the theory essentially based on the numerical simulation
Summary
Intensive efforts are currently being made to investigate materials exhibiting prominent quantum effects. In the simplest case of a spin-1/2 Heisenberg chain with antiferromagnetic interactions, the ground state is strongly entangled, lacks long-range order, and hosts fractionalized excitations called spinons [7] Those peculiar excitations, quite different from classical spin waves, possess a topological nature, can be understood as domain walls that disrupt the Néel order, and can be observed as a continuum in inelastic neutron scattering measurements. Such physics has been realized and probed in many different experimental realizations ranging from chains to ladders, e.g., in the quantum Heisenberg spin
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