The temperature dependence of excess conductivity σ′(Т) has been studied in three polycrystalline samples of the FeSe0.94 superconductor, prepared by different technologies. The measured temperature dependences of the Δ*(T) parameter, which is associated with the pseudogap in cuprates, were analyzed using the local pair model. At high temperatures, all three samples exhibit a high narrow maximum along Δ*(T) at Ts1∼250 K, which is typical for magnetic superconductors. Below T ≈ 225 K, the dependences Δ*(T) become different. Over almost the entire temperature range below Ts1, the S2 sample, prepared by solid state reaction without impurities, exhibits a Δ*(T) that is typical for Fe-pnictides. An exception is the interval between the structural change temperature Ts = 85 K and Tc, where this Δ*(T) exhibits an atypical, broad maximum. An analysis of the obtained dependence suggests the discovery of a pseudogap in this FeSe0.94 sample, below Ts. Samples S1, containing 4 wt.%Ag, and S3, having a nominal composition but containing nonsuperconducting hexagonal phase inclusions, both prepared by partial melting, show identical Δ*(T), but different from S2. They have a number of features that correlate with temperatures at which there are also features along M(T), and the Hall coefficient RH(T) changes signs several times with decreasing T, which indicates that there is change in the type of charge carriers in FeSe. The Δ*(T) dependence of the S3 sample below Ts has almost no maximum, since the nonsuperconducting impurities of the hexagonal phase in S3 prevent the formation of paired fermions near Tc. As a result, S3 also has the minimum local pair density = 0.26, determined by comparing Δ*(TG)/Δmax near Tc using the Peters–Bauer theory, whereas the dependence Δ*(T) does not follow the theory. S1 has the maximum = 0.47, supposedly due to the influence of Ag impurities. In S2, which is pure, ≈ 0.3, which is the same as that of YBa2Cu3O7−δ, and both dependences Δ*(Т) for S1 and S2 follow the theory over a wide temperature range.

中文翻译：

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FeSe 超导体中过度导电性和可能的​​赝隙的特征

已经在通过不同技术制备的 FeSe0.94 超导体的三个多晶样品中研究了过量电导率 σ'(Т) 的温度依赖性。使用局部对模型分析了与铜酸盐中的赝隙相关的 Δ*(T) 参数的测量温度依赖性。在高温下，所有三个样品都在 Ts1∼250 K 处沿 Δ*(T) 表现出高窄的最大值，这是磁超导体的典型特征。低于 T ≈ 225 K，相关性 Δ*(T) 变得不同。在低于 Ts1 的几乎整个温度范围内，通过不含杂质的固态反应制备的 S2 样品表现出典型的 Fe-pnictides Δ*(T)。一个例外是结构变化温度 Ts = 85 K 和 Tc 之间的间隔，其中该 Δ*(T) 表现出非典型的广泛最大值。对获得的相关性的分析表明在这个 FeSe0.94 样品中发现了一个低于 Ts 的赝隙。样品 S1 含有 4 wt.% Ag，样品 S3 具有标称成分但含有非超导六方相夹杂物，两者均通过部分熔化制备，显示相同的 Δ*(T)，但与 S2 不同。它们具有许多与温度相关的特征，其中也有沿 M(T) 的特征，并且霍尔系数 RH(T) 随着 T 的减小而多次改变符号，这表明电荷载流子的类型发生了变化在 FeSe。S3 样品在 Ts 以下的 Δ*(T) 依赖性几乎没有最大值，因为 S3 中六方相的非超导杂质阻止了 Tc 附近成对费米子的形成。因此，S3 也有最小局部对密度 = 0.26，通过使用 Peters-Bauer 理论比较 Tc 附近的 Δ*(TG)/Δmax 确定，而依赖关系 Δ*(T) 不遵循该理论。S1 具有最大值 = 0.47，推测是由于 Ag 杂质的影响。在纯 S2 中，≈ 0.3，与 YBa2Cu3O7−δ 相同，并且 S1 和 S2 的两个依赖关系 Δ*(Т) 在很宽的温度范围内都遵循理论。