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

¹ Institute of Physics - Hr-10 001 Zagreb, P.O. Box 304, Croatia
² CRTBT-CNRS - 38042 Grenoble Cedex 9, BP 166, France
³ IPA, EPFL - 1015 Lausanne, Switzerland

Received: 21 October 2002
Accepted: 14 March 2003

Abstract

Measurements of the magnetic susceptibility and its anisotropy in the quasi–one-dimensional system - in its low-T charge-density-wave (CDW) ground state are reported. Both sets of data reveal below 40 an extra paramagnetic contribution obeying a power law temperature dependence . 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 , strongly revives the case of random exchange spin chains. Introduced impurities (0.5% ) 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  atoms. We discuss the possibility that it is the charge frozen within a soliton-network below the glass transition determined recently in this system.