title: Thermopower and specific heat of the organic molecular salt (TMTSF)(2)ClO(4): observation of the narrow band response.
abstract: 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.
authors.affiliation: Physics Department, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
authors.forename: Cheng-Hai
authors.initials: CH
authors.lastname: Sun
authors.forename: Hong-Shun
authors.initials: HS
authors.lastname: Yang
authors.forename: Jian
authors.initials: J
authors.lastname: Liu
authors.forename: Hui-Xian
authors.initials: HX
authors.lastname: Gao
authors.forename: Jian-Bin
authors.initials: JB
authors.lastname: Wang
authors.forename: Lu
authors.initials: L
authors.lastname: Cheng
authors.forename: Lie-Zhao
authors.initials: LZ
authors.lastname: Cao
authors.forename: J C
authors.initials: JC
authors.lastname: Lasjaunias