Spin chain in magnetic field: limitations of the large-N mean-field theory

Abstract

Motivated by the recent success in describing the spin and orbital spectrum of a spin-orbital chain using a large-N mean-field approximation [Phys. Rev. B 91, 165102 (2015)], we apply the same formalism to the case of a spin chain in the external magnetic field. It occurs that in this case, which corresponds to N=2 in the approximation, the large-N mean-field theory cannot qualitatively reproduce the spin excitation spectra at high magnetic fields, which polarize more than 50% of the spins in the magnetic ground state. This, rather counterintuitively, shows that the physics of a spin chain can under some circumstances be regarded as more complex than the physics of a spin-orbital chain.

4 pages, 3 figures; appeared in the proceedings of the European Conference "Physics of Magnetism" (2014)

References in corpus (4)

• Spin-Orbital Separation in the quasi 1D Mott-insulator Sr2CuO3
• Dynamically dominant excitations of string solutions in the spin-1/2 antiferromagnetic Heisenberg chain in magnetic fields
• Von Neumann Entropy Spectra and Entangled Excitations in Spin-Orbital Models
• Spin-Dynamics of the antiferromagnetic S=1/2-Chain at finite magnetic Fields and intermediate Temperatures