Observation of a dimerized state in the S=1/2 quasi-one-dimensional antiferromagnet Sr14Cu24O41

We have performed magnetic susceptibility and electron spin resonance measurements on the quasi-one-dimensional magnet Sr14Cu24O41, which has simple chains and two-leg ladder chains of copper ions. The magnetic signals which we observed below room temperature mainly come from the simple chains. The experimental results show that the simple chain unexpectedly has a spin gap in the excitation spectrum, which originates from a dimerized state.