We report the discovery of a new three-dimensional (3D) topological Dirac semimetal (TDS) material KZnBi, coexisting with a naturally formed superconducting state on the surface under ambient pressure. Using photoemission spectroscopy together with first-principles calculations, a 3D Dirac state with linear band dispersion is identified. The characteristic features of massless Dirac fermions are also confirmed by magnetotransport measurements, exhibiting an extremely small cyclotron mass of $m^{*}=0.012$ $m_0$ and a high Fermi velocity of $v_F=1.04\times {10}^6\mathrm{m}/\mathrm{s}$. Interestingly, superconductivity occurs below 0.85 K on the (001) surface, while the bulk remains nonsuperconducting. The captured linear temperature dependence of the upper critical field suggests the possible non-$s$-wave character of this surface superconductivity. Our discovery serves a distinctive platform to study the interplay between 3D TDS and the superconductivity.

中文翻译：

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半金属 KZnBi 中表面超导和三维拓扑狄拉克态的共存

我们报告了一种新的三维 (3D) 拓扑狄拉克半金属 (TDS) 材料 KZnBi 的发现，该材料在环境压力下与表面自然形成的超导状态共存。使用光电发射光谱和第一性原理计算，确定了具有线性带色散的 3D Dirac 状态。无质量狄拉克费米子的特征也被磁传输测量证实，表现出极小的回旋质量${米}^{*}=0.012$ ${米}_0$ 和高费米速度 $v_F=1.04\times {10}^6\mathrm{米}/\mathrm{秒}$. 有趣的是，超导发生在 (001) 表面低于 0.85 K，而主体保持非超导。捕获的上临界场的线性温度依赖性表明可能的非$秒$- 这种表面超导性的波特征。我们的发现为研究 3D TDS 与超导性之间的相互作用提供了一个独特的平台。