Incommensurate systems as model compounds for disorder revealing low-temperature glasslike behavior.

We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C_{p}(T)/T^{3} law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T≈10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.

Thermopower and specific heat of the organic molecular salt (TMTSF)(2)ClO(4): observation of the narrow band response.

Measurements of thermopower S(a)(T) along the highly conducting a axis and specific heat of the Bechgaard salts (TMTSF)(2)ClO(4) for various cooling rates through the anion ordering temperature T(a) = 24 K were carried out. Sign reversal in S(a)(T) is found below T(a) and it decreases with increasing cooling rate, which is attributed to the change of a narrow band filling level as the temperature and the cooling rates change. The crossover from 2D to 3D in S(a)(T) is observed around 15 K. The onset temperature of anion ordering in S(a)(T) decreases from 29.8 to 24.2 K as the cooling rate increases. Meanwhile, the electronic specific heat coefficient γ has a pronounced change within this temperature region, giving strong evidence for a narrow band contribution. The difference in the specific heat between the quenched and relaxed states follows a T-cubic law from 5 to 24 K, implying a lattice distortion by the ordered anion only. The entropy estimated from the specific heat peak between 28 and 15 K is Rln (4/3) lower than the value Rln2, consistent with the thermopower result that some anions have been ordered far above T(a) for the relaxed state.

Interplay between phase defects and spin polarization in the specific heat of the spin-density-wave compound (TMTTF)2Br in a magnetic field.

Equilibrium heat relaxation experiments provide evidence that the ground state of the commensurate spin-density-wave compound (TMTTF)2Br after the application of a sufficient magnetic field is different from the conventional ground state. The experiments are interpreted on the basis of the local model of strong pinning as the deconfinement of soliton-antisoliton pairs triggered by the Zeeman coupling to spin degrees of freedom, resulting in a magnetic-field-induced density-wave glass for the spin carrying the phase configuration.

Evidence of 1D behavior of He4 confined within carbon-nanotube bundles.

We present the first low-temperature thermodynamic investigation of the controlled physisorption of He4 gas in carbon single-wall nanotube (SWNT) samples. The vibrational specific heat measured between 100 mK and 6 K demonstrates an extreme sensitivity to outgassing conditions. For bundles with a few number of nanotubes the extra contribution to the specific heat, C(ads), originating from adsorbed He4 at very low density displays 1D behavior, typical for He atoms localized within linear channels as grooves and interstitials, for the first time evidenced. For larger bundles, C(ads) recovers the 2D behavior akin to the case of He4 films on planar substrates (grafoil).