Bond Disorder in Even-Leg Heisenberg Ladders

Random bond disorder in antiferromagnetic spin-1/2 Heisenberg ladders is investigated using the Stochastic Series Expansion Quantum Monte Carlo method. We find that the effects of individual bond impurities vary strongly, depending on their position on legs and rungs. We initially focus on how the distribution of local bond energies depends on the impurity concentration. Then we study how the phase diagram of even-leg ladders is affected by random bond doping. We observe Bose glass phases in two regimes ($h^{\mathrm{\prime }}<h\lesssim h_{c1}$ and $h" < h <h_{c2}$) and a Bose-Einstein Condensate in-between. Their presence are discussed in the relation to the local bond energies.