Disappearance of the spin gap in a Zn-doped 2-leg ladder compound Sr(Cu1-xZnx)2O3

An inelastic neutron scattering study was performed on a Zn-substituted spin-1/2 Heisenberg 2-leg ladder compound Sr(Cu 1- x Zn x ) 2 O 3 ( x ≤0.04) to investigate nonmagnetic impurity effects on the quantum spin system with a large spin gap of approximately ∼400 K. The magnitude of the spin gap was found to be independent of Zn concentration, 33 meV, while the integrated magnetic scattering, which corresponds to the singlet-triplet excitation, decreased monotonically with increasing x . On account of the total-sum rule, this result supports the existence of a finite in-gap density of states at E = 0, which was suggested from the T -linear magnetic specific heat.