Quantum phase transition in coupled spin ladders

The ground state of an array of coupled, spin-1/2 antiferromagnetic ladders is studied using spin-wave theory, exact diagonalization (up to 36 sites), and quantum Monte Carlo techniques (up to 256 sites). Our results clearly indicate the occurrence of a zero-temperature phase transition between a Neel ordered and a nonmagnetic phase at a finite value of the interladder coupling (a(c)similar or equal to0.3). This transition is marked by remarkable changes in the structure of the excitation spectrum.