Phase diagram and critical properties of the frustrated Kondo necklace model in a magnetic field

The critical properties of the frustrated Kondo necklace model with a half saturation magnetization $\mathrm{}(m=1/2\mathrm{})\mathrm{}$ have been studied by means of an exact-diagonalization method. It is shown from bosonization technique that the model can be effectively expressed as a quantum sine-Gordon model. Thus it may show three (dimer plateau, Néel plateau and Tomonaga-Luttinger liquid) phases due to competitions among the Ising anisotropy $\Delta ,$ and the nearest- and next-nearest-neighbor exchange interactions $J_1$ and $J_2.$ The boundary lines on the $\Delta$-$J_2{/J}_1$ phase diagram separating the three phases are determined by the method of level spectroscopy, based on the conformal field theory.