Mixed-spin Heisenberg ladders in a magnetic field

In this work, we study alternating mixed-spin (s, S) Heisenberg ladders in the magnetic field h density matrix renormalization group and linear spin-wave calculations. The h versus interchain coupling J(perpendicular to) phase diagram for the (1/2, 1) case is investigated in detail. In particular, we demonstrate the compatibility between the critical line estimates and magnetic ordering by analyzing chains with variable values of J(perpendicular to) and of h along the chain, J(perpendicular to) and h scans, and considering the usual case of chains with uniform couplings. The magnetization plateau at 1/3 of saturation magnetization, 1/3 plateau, is observed for J(perpendicular to)> 0 and in a limited range for J(perpendicular to) < 0. The critical Kosterlitz-Thouless transition point, where the 1/3 plateau closes, is identified through a finite-size analysis of the transverse spin correlation functions.