Title: Dimer correlation amplitudes and dimer excitation gap in spin-1/2 XXZ and Heisenberg chains,
Abstract: Correlation functions of dimer operators, the product operators of spins on
two adjacent sites, are studied in the spin-$\frac{1}{2}$ XXZ chain in the
critical regime. The amplitudes of the leading oscillating terms in the dimer
correlation functions are determined with high accuracy as functions of the
exchange anisotropy parameter and the external magnetic field, through the
combined use of bosonization and density-matrix renormalization group methods.
In particular, for the antiferromagnetic Heisenberg model with SU(2) symmetry,
logarithmic corrections to the dimer correlations due to the
marginally-irrelevant operator are studied, and the asymptotic form of the
dimer correlation function is obtained. The asymptotic form of the spin-Peierls
excitation gap including logarithmic corrections is also derived.