We study the effects of a weakened link in random antiferromagnetic spin
chains. We show that healing occurs, and that homogeneity is restored at low
energy, in a way that is qualitatively similar to the fate of impurities in
clean ferromagnetic spin chains, or in Luttinger liquids with attractive
interactions. Healing in the random case occurs even without interactions, and
is characteristic of the random singlet phase. Using real space renormalization
group and exact diagonalization methods, we characterize this universal healing
crossover by studying the entanglement across the weak link. We identify a
crossover healing length L∗ that separates a regime where the system is cut
in half by the weak link from a fixed point where the spin chain is healed. Our
results open the way to the study of impurity physics in disordered spin
chains.Comment: 4.5 + 3 pages. 3 figure
