Long-lived magnons throughout the Brillouin zone of the strong-leg spin   ladder (C$_7$H$_{10}$N)$_2$CuBr$_4$
  Inelastic neutron scattering is used to measure spin excitations in fully deuterated single crystal samples of the strong-leg antiferromagnetic S=1/2 spin ladder compound (C$_7$H$_{10}$N)$_2$CuBr$_4$. Sharp resolution-limited magnons are observed across the entire one-dimensional Brillouin zone. The results validate the previously proposed {\it symmetric} spin ladder model and provide a reliable estimate of the relevant exchange interactions. 
D. Schmidiger and S. Muehlbauer and S. N. Gvasaliya and T. Yankova and   A. Zheludev
cond-mat.str-el