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arXiv 0905.3215cond-mat.supr-con
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Ba(Fe0 .93 Co0 .07)2 As2中磁场穿透深度的μ子自旋旋转测量:多个超导能隙的证据

Muon Spin Rotation Measurement of the Magnetic Field Penetration Depth in Ba(Fe0.93 Co0.07)2 As2 : Evidence for Multiple Superconducting Gaps

T. J. Williams, A. A. Aczel, E. Baggio-Saitovitch, S. L. Budko, P. C. Canfield, J. P. Carlo, T. Goko, J. Munevar, N. Ni, Y. J. Uemura, W. Yu, G. M. Luke

摘要:

在磁场沿$\hat{c}$方向的作用下,对Ba(Fe $_{0.93}$ Co $_{0.07})_2$ As $_2$)单晶进行了横场μ子自旋转动测量.傅立叶变换的测量光谱揭示了各向异性的线形特征的Abrikosov涡晶格。我们已经拟合$μ$ SRSR光谱的微观模型的渗透深度$λ$和金兹伯格-朗道参数$κ$。我们发现,作为温度的函数,穿透深度的变化比在标准的弱耦合BCS理论更迅速。出于这个原因,我们首先将温度依赖性拟合为幂律,其中当场从200 G变化到1000 G时,幂从1.6变化到2.2。由于功率和超流密度的场依赖性非常强,我们继续将温度依赖性拟合到两个间隙模型,其中两个间隙的大小与场无关。从这个模型中,我们得到了$2Δ_1=3.7k_BT_c$和$2Δ_2=1.6k_BT_c$的能隙,分别对应于大约6 meV和3 meV。

英文摘要:

We have performed transverse field muon spin rotation measurements of single crystals of Ba(Fe$_{0.93}$Co$_{0.07})_2$As$_2$ with the applied magnetic field along the $\hat{c}$ direction. Fourier transforms of the measured spectra reveal an anisotropic lineshape characteristic of an Abrikosov vortex lattice. We have fit the $μ$SRSR spectra to a microscopic model in terms of the penetration depth $λ$ and the Ginzburg-Landau parameter $κ$. We find that as a function of temperature, the penetration depth varies more rapidly than in standard weak coupled BCS theory. For this reason we first fit the temperature dependence to a power law where the power varies from 1.6 to 2.2 as the field changes from 200G to 1000G. Due to the surprisingly strong field dependence of the power and the superfluid density we proceeded to fit the temperature dependence to a two gap model, where the size of the two gaps is field independent. From this model, we obtained gaps of $2Δ_1=3.7k_BT_c$ and $2Δ_2=1.6k_BT_c$, corresponding to roughly 6 meV and 3 meV respectively.

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