Novel materials with both topological nontrivial states and superconductivity have attracted considerable attention in recent years. Single-crystal ${\mathrm{FeB}}_4$ was recently synthesized and demonstrated to exhibit superconductivity at temperatures lower than 2.9 K, and its nanoindentation hardness was measured to be 65 GPa. In this study, based on first-principles calculations and the low-energy $\mathit{k}·\mathit{p}$ effective Hamiltonian, we found that this $Pnnm$-type superhard ${\mathrm{FeB}}_4$ superconductor hosts topological behaviors with intersecting nodal rings (INRs) in the $k_x=0$ and $k_z=0$ planes and nodal wall states in the $k_y=\pi$ and $k_z=\pi$ planes. The observed surface drum-head-like (D-H-L) states on the [100] and [001] surfaces confirmed the presence of INR states in this system. According to our investigation results, ${\mathrm{FeB}}_4$, with its superconductivity, superior mechanical behaviors, one-dimensional and two-dimensional topological elements, and D-H-L surface states, is an existing single-phase target material that can be used to realize the topological superconducting state in the near future.

中文翻译：

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超硬超导体FeB4中的相交拓扑节点环和节点壁状态

近年来，具有拓扑非平凡状态和超导性的新型材料引起了相当大的关注。单晶${\mathrm{铁硼}}_4$最近合成并证明在低于 2.9 K 的温度下表现出超导性，其纳米压痕硬度为 65 GPa。在本研究中，基于第一性原理计算和低能$\mathit{克}·\mathit{磷}$ 有效的哈密顿量，我们发现这 $磷nn米$-型超硬 ${\mathrm{铁硼}}_4$ 超导体承载拓扑行为与交叉节点环（INRs）在 ${克}_X=0$ 和 ${克}_z=0$ 平面和节点壁状态 ${克}_{是}=\pi$ 和 ${克}_z=\pi$飞机。在 [100] 和 [001] 表面上观察到的表面鼓头状 (DHL) 状态证实了该系统中存在 INR 状态。根据我们的调查结果，${\mathrm{铁硼}}_4$凭借其超导性、优异的机械性能、一维和二维拓扑元素以及 DHL 表面态，是一种现有的单相靶材，可用于在不久的将来实现拓扑超导态。