Magnetic susceptibilities of integrable quantum ladders

As an extension of previous studies, we consider the magnetic susceptibilities of a coupled spinchain model at low temperature and of a more realistic model having a t - J ladder structure at zero temperature. The magnetic susceptibilities for both models are obtained numerically when the coupling constant is greater than its critical value. In this region, the ladders behave as a single chain for H < H_c and as two independent chains for H > H_c, showing a divergence at H_c. This divergence is expected to smear out at a finite temperature.