零和施加磁场下KFe2As2中的Specific heat
Specific heat in KFe2As2 in zero and applied magnetic field
摘要：
在剩余电阻率比为~650的单晶样品上测量了磷属铁族化合物超导体KFe_2As_2的比热，其起始比热为3.7K。零场正常态比热除以温度，C/T，通过坚持Tc处的外推正常态熵Sn（Tc）与Tc处的测量超导态熵Ss（Tc）之间的一致性，从Tc以上外推到T=0，因为对于二级相变，这两个熵必须相等。这种外推表明，这种相当干净的KFe_2As_2样品表现出非费米液体行为，即。e. C/T增加，在低温下，在与非费米液体的电阻率行为的报告。然而，作为磁场的函数的比热表明，在KFe 2As 2样品中常见的0.7 K附近的肩部特征不是先前提出的第二个超导能隙的证据，而是由于未知的磁性杂质相，这可能影响熵平衡和正常态比热的外推。具有类似场依赖性的该峰值（在幅度上稍大）也在较不纯的KFe 2As 2样品中发现，其剩余电阻率比仅为90，起始Tc=3.1 K。这些数据，结合在抑制超导性的场中测量的正常态比热，允许这样的结论，即正常态比热随着T->0的增加实际上在KFe 2As 2，i中没有看到。e.观察到费米液体行为。
英文摘要：
The specific heat down to 0.08 K of the iron pnictide superconductor KFe2As2 was measured on a single crystal sample with a residual resistivity ratio of ~650, with an onset Tc determined by specific heat of 3.7 K. The zero field normal state specific heat divided by temperature, C/T, was extrapolated from above Tc to T=0 by insisting on agreement between the extrapolated normal state entropy at Tc, Sn(Tc), and the measured superconducting state entropy at Tc, Ss(Tc), since for a second order phase transition the two entropies must be equal. This extrapolation would indicate that this rather clean sample of KFe2As2 exhibits non-Fermi liquid behavior, i. e. C/T increases at low temperatures, in agreement with the reported non-Fermi liquid behavior in the resistivity. However, specific heat as a function of magnetic field shows that the shoulder feature around 0.7 K, which is commonly seen in KFe2As2 samples, is not evidence for a second superconducting gap as has been previously proposed but instead is due to an unknown magnetic impurity phase, which can affect the entropy balance and the extrapolation of the normal state specific heat. This peak (somewhat larger in magnitude) with similar field dependence is also found in a less pure sample of KFe2As2, with a residual resistivity ratio of only 90 and an onset Tc=3.1 K. These data, combined with the measured normal state specific heat in field to suppress superconductivity, allow the conclusion that an increase in the normal state specific heat as T->0 is in fact not seen in KFe2As2, i. e. Fermi liquid behavior is observed.
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