Fractional power law susceptibility and specific heat in low-temperature insulating state of $\chem{o}$-$\chem{TaS_{3}}

• Published in: Europhysics letters Vol. 62; no. 4; pp. 554 - 560
• Main Authors: Biljaković, K., Miljak, M., Starešinić, D., Lasjaunias, J. C., Monceau, P., Berger, H., Levy, F.
• Format: Journal Article
• Language: English
• Published: EDP Sciences 01-05-2003
• Subjects: 71.45.Lr; 75.50.Lk
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/epl/i2003-00386-y

Measurements of the magnetic susceptibility and its anisotropy in the quasi–one-dimensional system $\chem{o}$-$\chem{TaS_{3}}$ in its low-T charge-density-wave (CDW) ground state are reported. Both sets of data reveal below 40$\un{K}$ an extra paramagnetic contribution obeying a power law temperature dependence $\chi(T)=AT^{-0.7}$. 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 $C_{\ab{LEE}}(0,T)=CT^{0.3}$, strongly revives the case of random exchange spin chains. Introduced impurities (0.5% $\chem{Nb}$) 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 $\chem{Ta}$ atoms. We discuss the possibility that it is the charge frozen within a soliton-network below the glass transition $T_{\ab{g}}\sim 40$ $\un{K}$ determined recently in this system.