Large-scale numerical evidence for Bose condensation in theS=1 antiferromagnetic chain in a strong field

Using the recently proposed density matrix renormalization group technique we show that the magnons in the S=1 antiferromagnetic Heisenberg chain effectively behave as bosons that condense at a critical field h₂. We determine the spin-wave velocity, v=2. 49 (1), as well as the gap =0. 4107 (1) J.