arXiv:cond-mat/0611772 · Physical Review B
Edge singularities in high-energy spectra of gapped one-dimensional magnets in strong magnetic fields
A. Friedrich, Alexei K. Kolezhuk, Ian P. McCulloch, Ulrich Schollwöck
Abstract
We use the dynamical density matrix renormalization group technique to show that the high-energy part of the spectrum of an $S=1$ Heisenberg chain, placed in a strong external magnetic field $H$ exceeding the Haldane gap $\ensuremath{\Delta}$, contains edge singularities, similar to those known to exist in the low-energy spectral response. It is demonstrated that in the frequency range $\ensuremath{\omega}\ensuremath{\gtrsim}\ensuremath{\Delta}$ the longitudinal (with respect to the applied field) dynamical structure factor is dominated by the power-law singularity ${S}^{\ensuremath{\Vert}}(q=\ensuremath{\pi},\ensuremath{\omega})\ensuremath{\propto}{(\ensuremath{\omega}\ensuremath{-}{\ensuremath{\omega}}_{0})}^{\ensuremath{-}{\ensuremath{\alpha}}^{\ensuremath{'}}}$. We study the behavior of the high-energy edge exponent ${\ensuremath{\alpha}}^{\ensuremath{'}}$ and the edge ${\ensuremath{\omega}}_{0}$ as functions of the magnetic field. The existence of edge singularities at high energies is directly related to the Tomonaga-Luttinger liquid character of the ground state at $H>\ensuremath{\Delta}$ and is expected to be a general feature of one-dimensional gapped spin systems in high magnetic fields.