Specific heat measurements of the lattice contribution and spin-density-wave transition in (TMTSF)2X (X = PF6 and AsF6) and (TMTTF)2Br salts
Specific heat measurements of the lattice contribution and spin-density-wave transition in (TMTSF)2X (X = PF6 and AsF6) and (TMTTF)2Br salts
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(TMTSF)2X（X = PF6 和 AsF6）和 (TMTTF)2Br 盐中晶格贡献和自旋密度波跃迁的比热测量
DOI：
10.1088/0953-8984/11/26/310
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
P. Monceau
中科院分区：
文献类型：
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作者：
H. Yang;J. Lasjaunias;P. Monceau
测量了准一维有机化合物（TMTSF）2X （X = PF6， AsF6和ClO4）和（TMTTF）2Br在1.8 ~ 40 K范围内的比热。晶格贡献仅在低于3k的小温度范围内遵循T3定律，并且每种化合物在7.0 K左右（(TMTSF)2ClO4为4 K）时C/T3有典型的波动。我们将这种行为解释为声子维度从低t三维行为向高于3k的低维t行为（从= 2.3到2.5）的交叉，加上两个与远红外光谱检测到的软晶格模式频率一致的额外爱因斯坦模式。化合物（TMTSF）2PF6、（TMTSF）2AsF6和（TMTTF）2Br的自旋密度波（SDW）转变温度分别为12.2、12.4和11.7 K。SDW转变异常的幅度分别为总比热的4.5%、2.5%和小于1%。（TMTSF）2PF6的比热异常的幅度太大，不能单独用电子自旋贡献来解释，这意味着晶格也参与了跃迁。从我们的精确测量中，我们确认SDW转变是一个二阶转变，没有任何一阶特征，如滞后和潜热。发现比热在整个测量温度范围内与时间有关，因为它的值对所有三种化合物的动力学过程非常敏感。
The specific heats of the quasi-one-dimensional organic compounds (TMTSF)2X (X = PF6, AsF6 and ClO4) and (TMTTF)2Br were measured over the temperature range from 1.8 to 40 K. The lattice contribution follows a T3-law only in a small temperature range below 3 K, and shows a typical bump in C/T3 at about 7.0 K for every compound (4 K for (TMTSF)2ClO4). We interpret this behaviour as a phonon dimensionality crossover from a low-T tridimensional behaviour, towards a lower-dimensionality T-behaviour (with = 2.3 to 2.5) above 3 K, plus two additional Einstein modes in agreement with the frequencies of soft lattice modes detected by far-infrared spectroscopy. The spin-density-wave (SDW) transition temperature was found to take the values 12.2, 12.4 and 11.7 K for the compounds (TMTSF)2PF6, (TMTSF)2AsF6 and (TMTTF)2Br, respectively. The magnitude of the SDW transition anomaly is 4.5%, 2.5% and less than 1% of the total specific heat for each sample, respectively. The magnitude of the specific heat anomaly for (TMTSF)2PF6 is too large to be explained by the electron spin contribution alone, which implies that the lattice is also involved in the transition. From our accurate measurements, we confirm that the SDW transition is a second-order transition without any characteristics of first order, like hysteresis and latent heat. The specific heat was found to be time dependent over the whole measurement temperature range as its value is quite sensitive to the kinetics process for all three compounds.