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

TL;DR

This study investigates the low-temperature magnetic susceptibility and specific heat of o-TaS_{3}, revealing power-law behaviors suggestive of random exchange spin chains and localized two-level systems, with implications for charge dynamics below 40 K.

Contribution

It provides the first detailed analysis of magnetic susceptibility anisotropy and specific heat in o-TaS_{3} at low temperatures, linking these to TLS models and soliton-network charge freezing.

Findings

Power-law magnetic susceptibility with exponent -0.7 below 40 K.

Specific heat follows a power law with exponent 0.3, indicating low-energy excitations.

Impurities increase amplitude but not the power-law exponent.

Abstract

Measurements of the magnetic susceptibility and its anisotropy in the quasi-one-dimensional system o-TaS_{3} 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 \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_{LEE}(0,T)=CT^{0.3}, 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 per cca 900 Ta atoms. We discuss the possibility that it is the charge frozen within a soliton-network below the glass transition T_{g}~40 K determined recently in this system.