Thermodynamic properties and elementary excitations in S=1/2
one-dimensional Heisenberg antiferromagnet KCuGaF6 were investigated by
magnetic susceptibility, specific heat and ESR measurements. Due to the
Dzyaloshinsky-Moriya interaction with alternating D-vectors and/or the
staggered g-tensor, the staggered magnetic field is induced when subjected to
external magnetic field. Specific heat in magnetic field clearly shows the
formation of excitation gap, which is attributed to the staggered magnetic
field. The specific heat data was analyzed on the basis of the quantum
sine-Gordon (SG) model. We observed many ESR modes including one soliton and
three breather excitations characteristic of the quantum SG model.Comment: 4 pages, 5 figures, to appear in J. Phys. Soc. Jpn., vol. 76, no.