Fractional power law susceptibility and specific heat in low-temperature insulating state of o-TaS3

Measurements of the magnetic susceptibility and its anisotropy in the quasi–one-dimensional system o-TaS3 in its low-T charge-density-wave (CDW) ground state are reported. Both sets of data reveal below 40 K an extra paramagnetic contribution obeying a power law temperature dependence χ(T) = AT−0.7. The fact that the extra term measured previously in specific heat in zero field, ascribed to low-energy CDW excitations, also follows a power law CLEE(0,T) = CT0.3, strongly revives the case of random exchange spin chains. Introduced impurities (0.5% Nb) only increase the amplitude C, but do not change essentially the exponent. Within the two-level system (TLS) model, we estimate from the amplitudes A and C that there is one TLS with a spin s = 1/2 localized on the chain at the lattice site on average every 900 Ta atoms. We discuss the possibility that it is the charge frozen within a soliton-network below the glass transition Tg ∼ 40 K determined recently in this system.