邻晶面上原子层超导体中约瑟夫森涡旋的各向异性输运
Anisotropic transport of Josephson vortices in atomic-layer superconductors on vicinal surfaces
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中文总结 AI 辅助
该研究针对邻晶面原子层超导体Si(111)-($\sqrt{7}\times\sqrt{3}$)-In，观测到约瑟夫森涡旋的各向异性输运，揭示其在不同温度磁场下的输运机制，构建了$B$-$T$相图。
中文摘要 AI 辅助
原子台阶对表面二维超导体有强烈影响。磁场下在原子台阶处形成的约瑟夫森涡旋可能主导低温下的输运现象，但其实验验证仍缺乏。本文报道了具有邻晶面的原子层超导体Si(111)-($\sqrt{7}\times\sqrt{3}$)-In的涡旋输运性质，通过扫描隧道显微镜直接观测到该体系中的约瑟夫森涡旋。在面外磁场$B$下检测到，电阻随温度$T$降低而急剧下降，且呈现出相对于原子台阶方向的显著各向异性，与涡旋迁移率成正比的面电阻各向异性在中等磁场下达到$10^3$量级。在高温低$B$区域，约瑟夫森涡旋表现出热激发的蠕变运动，具有各向异性的激活能$U_{\mathrm{act}}$；$B$进一步增大时，$U_{\mathrm{act}}$各向异性地被抑制至零，在$0.10 \lesssim B \lesssim 0.20$ T区间形成一维无钉扎涡旋流；最低温度下，涡旋运动由量子隧穿主导。基于这些测量构建的$B$-$T$相图揭示了多个具有方向依赖涡旋输运机制的区域。
英文摘要
Atomic steps have strong influences on surface two-dimensional superconductors. Josephson vortices formed at the atomic steps under magnetic fields may dominate transport phenomena at low temperatures, but its experimental verification is still lacking. Here, we report the vortex transport properties of atomic-layer superconductor Si(111)-$(\sqrt{7}\times\sqrt{3})$-In with vicinal surfaces, for which Josephson vortices are directly observed by scanning tunneling microscopy. A sharp drop in resistance with decreasing temperature $T$, detected under out-of-plane magnetic field $B$, reveals a distinctive anisotropy with respect to the atomic step direction. The anisotropy of sheet resistance, proportional to that of vortex mobility, amounts to the order of $10^3$ at intermediate magnetic fields. In the high-$T$ and low-$B$ region, Josephson vortices exhibit thermally excited creep motions with anisotropic activation energy $U_\mathrm{act}$. A further increase in $B$ suppresses $U_\mathrm{act}$ toward zero anisotropically, resulting in one-dimensional pinning-free vortex flow at $0.10 \lesssim B \lesssim 0.20$ T. At the lowest temperatures, the vortex motion is governed by quantum tunneling. A $B$-$T$ phase diagram constructed based on these measurements reveals multiple regions characterized by directionally dependent vortex-transport mechanisms.
