engleski

Low-temperature thermodynamical properties of Bechgaard salts: (TMTSF)_2PF_6 versus (TMTSF)_2AsF_6

We report on specific heat measurements of (TMTSF)_2AsF_6 in the temperature range 75 mK to 7 K and compare them with the results obtained for (TMTSF)_2PF_6. In addition to the generic features of density waves (DW) heat capacities, there are similar discontinuities in the lattice contribution in both systems at 1.9 K and 3.5 K, which we ascribe to transitions between sub-SDW phases. The low-energy excitations (LEE) contribution, dominant at T<0.5K, is strongly reduced in the case of AsF_6 as well as the time dependent effects in the specific heat. We discuss the origin of the hyperfine T^2 term and give the arguments that it can only be provided by the metastable LEEs. Finally, we relate similarities, but also differences, of the specific properties of mixed CDW/SDW states which has been recently found in structural investigations of both compounds.

lattice and electronic heat capacity of solids; phonon states and bands; normal modes; and phonon dispersion; collective modes; low-dimensional conductors; spin-density waves in magnetically ordered materials

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