Exotic ground state of η-Na9/7V2O5

The nature of the ground gapped state in the novel quasi-one-dimensional compound η-Na9/7V2O5 is rather mysterious, if one takes into account the odd number of spins on each structural element. Combining the results of specific heat, susceptibility, electron spin resonance and dielectric conductivity measurements we show that it can be understood in terms of multi-spin objects building up a linear chain. In spite of the small total spin, their spatial extent results in an exchange constant comparable to the one in the non-dimerized state. (orig.)