Large-scale numerical evidence for Bose condensation in the S=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 hc. We determine the spin-wave velocity, v=2.49(1), as well as the gap Δ=0.4107(1)J.