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arXiv 1111.5025cond-mat.supr-con
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用实验和半经验方法确定准二维超导体中的Pauli极限场并应用于$κ$ -(BEDT-TTF)$_2$ Cu(NCS)$_2$:FFLO态的有力证据

An Experimental and Semi-Empirical Method to Determine the Pauli-Limiting Field in Quasi 2D Superconductors as applied to $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$: Strong Evidence of a FFLO State

C. C. Agosta, Jing Jin, W. A. Coniglio, B. E. Smith, K. Cho, I. Stroe, C. Martin, S. W. Tozer, T. P. Murphy, E. C. Palm, J. A. Schlueter, M. Kurmoo

摘要:

我们提出了上临界场数据$κ$ -(BEDT-TTF)$_2$ Cu(NCS)$_2$的磁场接近平行和平行于导电层。我们表明,我们可以消除这些层状材料中的涡旋动力学的影响,如果层的取向在0.3度的平行于所施加的磁场。消除涡旋效应后,数据中留下一个剩余特征,对应于泡利顺磁极限($H_p$)。提出了一种计算准二维超导体中$H_p$的半经验方法。该方法考虑了每个准二维超导体的能隙,这是从比热数据计算,和许多体效应的影响。计算的泡利顺磁极限,然后比较标题化合物和其他有机导体的临界场数据。许多被研究的准二维超导体,包括上述有机超导体和CeCoIn $_5$,表现出超过其计算的$H_p$的上临界场,表明非常规的超导性。结果表明,$κ$ -(BEDT-TTF)$_2$ Cu(NCS)$_2$的高场低温态与Fulde Ferrell Larkin Ovchinnikov态一致.

英文摘要:

We present upper critical field data for $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$ with the magnetic field close to parallel and parallel to the conducting layers. We show that we can eliminate the effect of vortex dynamics in these layered materials if the layers are oriented within 0.3 degrees of parallel to the applied magnetic field. Eliminating vortex effects leaves one remaining feature in the data that corresponds to the Pauli paramagnetic limit ($H_p$). We propose a semi-empirical method to calculate the $H_p$ in quasi 2D superconductors. This method takes into account the energy gap of each of the quasi 2D superconductors, which is calculated from specific heat data, and the influence of many body effects. The calculated Pauli paramagnetic limits are then compared to critical field data for the title compound and other organic conductors. Many of the examined quasi 2D superconductors, including the above organic superconductors and CeCoIn$_5$, exhibit upper critical fields that exceed their calculated $H_p$ suggesting unconventional superconductivity. We show that the high field low temperature state in $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$ is consistent with the Fulde Ferrell Larkin Ovchinnikov state.

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