Effects of substituting rare-earth ion R by non-magnetic impurities in $R_{2}BaNi{O}_5$ - theory and numerical DMRG results

In this paper we study the effect of substituting R (rare-earth ion) by non-magnetic ions in the spin-1 chain material $R_{2}BaNi{O}_5$. Using a strong-coupling expansion and numerical density matrix renormalization group calculations, we show that spin-wave bound states are formed at the impurity site. Experimental consequences of the bound states are pointed out.