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 (mu SR) measurements of the spin S = 1/2 antiferromagnetic Heisenberg chain material SrCuO2. We find that in a weak applied magnetic field B-0 the spin-lattice relaxation rate lambda follows a power law lambda alpha B-0(-n) 0 with n = 0.9(3). This result is temperature independent for 5 K <= T <= 300 K. Within conformal field theory and using the Muller ansatz we conclude ballistic spin transport in SrCuO2.