Quantum chaos in spin-1/2 two-leg ladders

In this paper, we study numerically the emergence of quantum chaos in the antiferromagnetic (AF) Heisenberg two-leg spin-1/2 ladder. We investigate the mutual effects of magnetic defects and couplings (rung or leg) on the statistical properties of the energy spectrum using the exact diagonalization technique. The system is chaotic when the leg and rung coupling strengths are equal, and even adding a strong magnetic defect does not change the energy distribution. Introducing two defects also does not change the level spacing distribution. We conclude that the system not strongly depend on the number of defects. However, when one of the couplings (rung or leg) is much larger than the other, level spacing distribution shows a profound dependence on it and a transition from chaotic to the integrable regime is found.