用于小磁性粒子研究的亚微米Nb/HfTi/Nb结超导量子干涉器件
Superconducting quantum interference devices with submicron Nb/HfTi/Nb junctions for investigation of small magnetic particles
摘要：
在$4.2\,\mathrm{K}$温度下，研究了基于HfTi势垒的亚微米约瑟夫森结的小型化Nb直流超导量子干涉器件（SQUID）的电输运、磁通噪声和自旋灵敏度。SQUID的布局是磁力计型或梯度型。在白噪声区，对于最佳磁强计，我们得到磁通噪声$S_Φ^{1/2}=250\,\mathrm{n}Φ_0/\mathrm{Hz}^{1/2}$，对应于自旋灵敏度$S^{1/2}_μ\,\ge\,29\,μ_B/\mathrm{Hz}^{1/2}$。对于梯度计，我们发现$S_Φ^{1/2}=300\,\mathrm{n}Φ_0/\mathrm{Hz}^{1/2}$和$S^{1/2}_μ\,\ge\,44\,μ_B/\mathrm{Hz}^{1/2}$。这些器件仍然可以在磁通噪声和磁性粒子与SQUID之间的耦合方面进行优化，从而为进一步改进单自旋分辨率留下空间。
英文摘要：
We investigated, at temperature $4.2\,\mathrm{K}$, electric transport, flux noise and resulting spin sensitivity of miniaturized Nb direct current superconducting quantum interference devices (SQUIDs) based on submicron Josephson junctions with HfTi barriers. The SQUIDs are either of the magnetometer-type or gradiometric in layout. In the white noise regime, for the best magnetometer we obtain a flux noise $S_Φ^{1/2}=250\,\mathrm{n}Φ_0/\mathrm{Hz}^{1/2}$, corresponding to a spin sensitivity $S^{1/2}_μ\,\ge\,29\,μ_B/\mathrm{Hz}^{1/2}$. For the gradiometer we find $S_Φ^{1/2}=300\,\mathrm{n}Φ_0/\mathrm{Hz}^{1/2}$ and $S^{1/2}_μ\,\ge\,44\,μ_B/\mathrm{Hz}^{1/2}$. The devices can still be optimized with respect to flux noise and coupling between a magnetic particle and the SQUID, leaving room for further improvement towards single spin resolution.
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