标题： II型超导体中超导性的空间分辨 显示英文标题

标题： Spatially resolving superconductivity in type-II superconductors

摘要： 超导性通过宏观零电阻态的出现来识别，通常通过在有限电流下四探针电压消失来推断。这种推断假设了空间均匀的导电性——例如，在电流引线和采样有限电势梯度的电压电极之间至少存在一条连续的超导路径——如果驱动电流绕过电极或狭窄的细丝短路电流接触，这种推断可能会失败。在这里，我们介绍了一种方法，通过使用低温导电原子力显微镜（cAFM）对局部直流变化进行空间分辨测量，来测试这些假设。使用Fe(Se,Te)作为模型系统，我们发现尽管体测量与均匀超导态一致，但该材料表现出异质的导电景观：微米尺度的超导区域与相对绝缘的区域共存。我们进一步表明，cAFM在20 K（> TC）时解析出导电性波动，这些波动在重复扫描中变化，符合BCS-BEC交叉区域中短暂存在的预形成库珀对的预期。这些结果确立了cAFM作为一种实用工具，用于验证四探针输运背后的假设，并强调了在宏观响应可能掩盖纳米尺度不均匀性的材料中进行直接空间探测的必要性。准确识别宏观特性对于由其宏观特性定义的材料类别如超导体至关重要。 显示英文摘要

摘要： Superconductivity is identified by the emergence of a macroscopic zero-resistance state, typically inferred from a vanishing four-probe voltage at finite current. That inference assumes spatially uniform conduction-e.g., at least one continuous superconducting path between the current leads and voltage electrodes that sample a finite potential gradient-and can fail if the drive current bypasses the electrodes or if narrow filaments short the current contacts. Here we introduce a methodology to test these assumptions in superconductors, by using spatially resolved measurements of local variations in dc using cryogenic conductive atomic-force microscopy (cAFM). Using Fe(Se,Te) as a model system, we find that despite bulk measurements consistent with a homogeneous superconducting state, the material exhibits a heterogeneous conducting landscape: micrometre-scale superconducting regions coexist with relatively insulating areas. We further show that cAFM resolves conductance fluctuations at 20 K (> TC) that vary between repeated scans, consistent with expectations for short-lived, pre-formed Cooper pairs in the BCS-BEC crossover regime. These results establish cAFM as a practical tool to validate assumptions underlying four-probe transport and underscore the need for direct spatial probes in materials whose macroscopic response can conceal nanoscale inhomogeneity. Accurate identification of macroscopic properties is critical for materials classes like superconductors that are defined by their macroscopic properties.