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Specific heat in KFe_2As_2 in zero and applied magnetic field

机译：零磁场和施加磁场中KFe_2As_2中的比热

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摘要

The specific heat down to 0.08 K of the iron pnictide superconductor KFe_2 AS_2 was measured on a single-crystal sample with a residual resistivity ratio of ～650, with a T_c~(onset) determined by a specific heat of 3.7 K. The zero-field normal-state specific heat divided by temperature, C/T, was extrapolated from above T_c to T = 0 by insisting on agreement between the extrapolated normal-state entropy at T_c, S_n~(extrap)(T_C), and the measured superconducting-state entropy at T_c, S_s~(meas)(Tc), since for a second-order phase transition the two entropies must be equal. This extrapolation would indicate that this rather clean sample of KFe_2As_2 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 KFe_2As_2 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 KFe_2As_2, with a residual resistivity ratio of only 90 and T_c~(onset) = 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 KFe_2As_2; i.e., Fermi-liquid behavior is observed.
机译：在残留电阻率约为650的单晶样品上测量了铁素超导KFe_2 AS_2的低至0.08 K的比热，T_c〜（开始）由比热3.7 K确定。零-通过坚持在T_c处外推的常态熵，S_n〜（extrap）（T_C）和测得的超导之间的一致性，将场常态比热除以温度C / T从T_c之上推算为T = 0 T_c，S_s_（meas）（Tc）处的状态熵，因为对于二阶相变，两个熵必须相等。这种推论表明，这种相当纯净的KFe_2As_2样品表现出非费米液体行为。即在低温下C / T升高，这与报道的电阻率非费米液体行为一致。然而，作为磁场的函数的比热表明，在KFe_2As_2样品中通常看到的在0.7 K附近的肩部特征不能像先前提出的那样证明存在第二个超导间隙，而是由于未知的磁性杂质相，这会影响熵平衡和常态比热的外推。在不太纯净的KFe_2As_2样品中也发现了具有类似场依赖关系的该峰值（幅度稍大），其剩余电阻率仅为90，T_c〜（起始）= 3.1K。场中的比热抑制超导性，可以得出这样的结论：实际上在KFe_2As_2中看不到T→0时常态比热的增加。即，观察到费米-液行为。

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  • 来源
    《Physical review》 |2011年第17期|p.172502.1-172502.4|共4页
  • 作者

    J. S. Kim; E. G. Kim; G. R. Stewart; X. H. Chen; X. F. Wang;

  • 作者单位

    Department of Physics, University of Florida, Gainesville, Florida 32611, USA;

    Department of Physics, University of Florida, Gainesville, Florida 32611, USA;

    Department of Physics, University of Florida, Gainesville, Florida 32611, USA;

    Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China;

    Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China;

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  • 关键词

    thermodynamic properties; non-fermi-liquid ground states, electron phase diagrams and phase transitions in model systems;

    机译：热力学性质;模型系统中的非费米液体基态;电子相图和相变;

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