Low temperature ballistic spin transport in the S=1/2 antiferromagnetic   Heisenberg chain compound SrCuO2
  We report zero and longitudinal magnetic field muon spin relaxation measurements of the spin S=1/2 antiferromagnetic Heisenberg chain material SrCuO2. We find that in a weak applied magnetic field B the spin-lattice relaxation rate follows a power law B^n with n=-0.9(3). This result is temperature independent for 5K < T < 300 K. Within conformal field theory and using the M\"uller ansatz we conclude ballistic spin transport in SrCuO2. 
H. Maeter, A. A. Zvyagin, H. Luetkens, G. Pascua, Z. Shermadini, R.   Saint-Martin, A. Revcolevschi, C. Hess, B. B\"uchner, ...
cond-mat.str-el