Using a combined analytical and numerical approach, we study the collective spin and orbital excitations in a spin-orbital chain under a crystal field. Irrespective of the crystal-field strength, these excitations can be universally described by fractionalized fermions. The fractionalization phenomenon persists and contrasts strikingly with the case of a spin chain, where fractionalized spinons cannot be individually observed but confined to form magnons in a strong magnetic field. In the spin-orbital chain, each of the fractional quasiparticles carries both spin and orbital quantum numbers, and the two variables are always entangled in the collective excitations. Our result further shows that the recently reported separation phenomenon occurs when crystal fields fully polarize the orbital degrees of freedom. In this case, however, the spinon and orbiton dynamics are decoupled solely because of a redefinition of the spin and orbital quantum numbers.Using a combined analytical and numerical approach, we study the collective spin and orbital excitations in a spin-orbital chain under a crystal field. Irrespective of the crystal-field strength, these excitations can be universally described by fractionalized fermions. The fractionalization phenomenon persists and contrasts strikingly with the case of a spin chain, where fractionalized spinons cannot be individually observed but confined to form magnons in a strong magnetic field. In the spin-orbital chain, each of the fractional quasiparticles carries both spin and orbital quantum numbers, and the two variables are always entangled in the collective excitations. Our result further shows that the recently reported separation phenomenon occurs when crystal fields fully polarize the orbital degrees of freedom. In this case, however, the spinon and orbiton dynamics are decoupled solely because of a redefinition of the spin and orbital quantum numbers.

arXiv:1402.3255Physical Review BApr 2, 201524 citations

Elementary Excitations of the Symmetric Spin-Orbital Model: The XY Limit

Frédéric Mila, Beat Frischmuth, Andreas Deppeler +1 more

The elementary excitations of the 1D, symmetric, spin-orbital model are studied in two anisotropic cases: the pure $\mathrm{XY}$ and the dimerized $\mathrm{XXZ}$ models. While they preserve the symmetry between spin and orbital degrees of freedom, these models allow for a picture of the low-lying excitations. In the pure $\mathrm{XY}$ case, a phase separation takes place between two phases with free-fermion-like gapless excitations. In the dimerized case the low-energy effective Hamiltonian reduces to the 1D Ising model with gapped excitations. All the elementary excitations involve simultaneous flips of the spin and orbital degrees of freedom: a clear indication of the breakdown of the traditional mean-field theory.The elementary excitations of the 1D, symmetric, spin-orbital model are studied in two anisotropic cases: the pure $\mathrm{XY}$ and the dimerized $\mathrm{XXZ}$ models. While they preserve the symmetry between spin and orbital degrees of freedom, these models allow for a picture of the low-lying excitations. In the pure $\mathrm{XY}$ case, a phase separation takes place between two phases with free-fermion-like gapless excitations. In the dimerized case the low-energy effective Hamiltonian reduces to the 1D Ising model with gapped excitations. All the elementary excitations involve simultaneous flips of the spin and orbital degrees of freedom: a clear indication of the breakdown of the traditional mean-field theory.

arXiv:cond-mat/9809094Physical Review LettersMay 3, 199926 citations

Bipartite entanglements in spin–orbital systems

Dongmeng Chen, Weihua Wang, Liang‐Jian Zou

Physics Letters AJan 15, 20103 citations

Dynamical properties of spin-orbital chains in a magnetic field

Weiqiang Yu, Stephan Haas

The excitation spectrum of the one-dimensional spin-orbital model in a magnetic field is studied, using a recently developed dynamical density-matrix renormalization-group technique. The method is applied to chains with up to 80 sites, and examined for test cases such as the one-dimensional spin-1/2 Heisenberg antiferromagnet whose excitation spectrum is known exactly from the Bethe ansatz. In the spin-orbital chain, the characteristic dynamical response depends strongly on the model parameters and the applied magnetic field. The coupling between the spin and orbital degrees of freedom is found to influence the incommensuration at finite magnetizations. In the regions of the phase diagram with only massive spin and orbital excitations, a finite field is required to overcome the spin gap. An orbital mode is found to become massless in this partially spin-polarized regime, indicating a strong coupling between the two degrees of freedom. In the critical region with three elementary gapless excitations, a prominent particle-hole excitation is observed at higher energies, promoted by the biquadratic term in the model Hamiltonian of the spin-orbital chain.The excitation spectrum of the one-dimensional spin-orbital model in a magnetic field is studied, using a recently developed dynamical density-matrix renormalization-group technique. The method is applied to chains with up to 80 sites, and examined for test cases such as the one-dimensional spin-1/2 Heisenberg antiferromagnet whose excitation spectrum is known exactly from the Bethe ansatz. In the spin-orbital chain, the characteristic dynamical response depends strongly on the model parameters and the applied magnetic field. The coupling between the spin and orbital degrees of freedom is found to influence the incommensuration at finite magnetizations. In the regions of the phase diagram with only massive spin and orbital excitations, a finite field is required to overcome the spin gap. An orbital mode is found to become massless in this partially spin-polarized regime, indicating a strong coupling between the two degrees of freedom. In the critical region with three elementary gapless excitations, a prominent particle-hole excitation is observed at higher energies, promoted by the biquadratic term in the model Hamiltonian of the spin-orbital chain.

arXiv:cond-mat/0005526Physical review. B, Condensed matterDec 20, 200013 citations

Entanglement in Spin Chains

K. Sengupta

arXiv:2109.02657Quantum science and technologyJan 1, 202232 citations

The elementary excitations of the 1D, symmetric, spin-orbital model are studied in two anisotropic cases: the pure

\mathrm{XY}

and the dimerized

\mathrm{XXZ}

models. While they preserve the symmetry between spin and orbital degrees of freedom, these models allow for a picture of the low-lying excitations. In the pure

\mathrm{XY}

case, a phase separation takes place between two phases with free-fermion-like gapless excitations. In the dimerized case the low-energy effective Hamiltonian reduces to the 1D Ising model with gapped excitations. All the elementary excitations involve simultaneous flips of the spin and orbital degrees of freedom: a clear indication of the breakdown of the traditional mean-field theory.