Jun-ichiro KISHINE
[J. Phys. Soc. Jpn. 66, 1229 (1997)]
Recently it was reported that the Gaussian spin-echo decay rate, T2G-1, of the S=1/2 Heisenberg two-leg ladder SrCu2O3 reveals a very weak temperature dependence and saturates at T=0. A calculation using a quantum Monte Carlo technique shows reasonable agreement with experimental results. However it remains unclear how the spin echo decay process reflects the magnetic coherence of the system, especially why T2G-1 saturates at T=0. To clarify this point without any assumption on the magnetic coherence of the system, we calculated T2G-1 based on the Majorana fermion representation of the Heisenberg two-leg ladder Hamiltonian introduced by Shelton et al. In conclusion, the magnetic coherence of the system is clearly described in terms of the condensation of the Majorana fermions into the pair condensed phase with gapfull excitations and the saturation of T2G-1 at T=0 can be explained by the remaining pair creation process from the condensate.