论文标题
岩石碳化物NBC和TAC的超导性和拓扑方面
Superconductivity and topological aspects of the rock-salt carbides NbC and TaC
论文作者
论文摘要
具有非平凡带结构的超导材料是拓扑超导性的潜在候选物。在这里，通过将Muon-Spin旋转和松弛（$μ$ SR）的方法与理论计算相结合，我们研究了岩石盐型化合物NBC和TAC的超导和拓扑特性（分别为$ T_C $ = 11.5和10.3 K）。在宏观水平上，NBC和TAC的磁场测量值分别为1.93和0.65 t的磁容器测量，分别为1.93和0.65 t。低温超流体密度，由横向场$μ$ $ sr和电子特异性数据确定，这表明在NBC和TAC中均具有完全传播的超导状态，其零温度gap $Δ_0= 1.90 $ = 1.90 $和1.45 meV，并且磁性渗透渗透性渗透率深度为$λ_0$ = 141和77 nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nm nmm nmm nmm nmm nmm nmm nmm nmm nmm nmm nmm。频道结构计算表明，费米级别的状态密度由NB $ 4D $ - （或TA $ 5D $ - ）轨道主导，这些轨道与C $ P $ - 轨道强烈杂交，以产生大缸状的Fermi表面，类似于与高$ T_C $ T_C $ T_C $ TO_C $ IRAIDER-IRAIND IRAIN-IRAIDER基超级尺寸相似。在不考虑自旋轨道耦合（SOC）效果的情况下，第一个Brillouin区域包含散装带结构中的三个封闭节点线，受时间反转和空间内传感对称性保护。在考虑SOC时，其在NBC案例中的影响显得相当谦虚。因此，可以将节点线保存在NBC中，因此将其作为潜在的拓扑超导体。
Superconducting materials with a nontrivial band structure are potential candidates for topological superconductivity. Here, by combining muon-spin rotation and relaxation ($μ$SR) methods with theoretical calculations, we investigate the superconducting and topological properties of the rock-salt-type compounds NbC and TaC (with$T_c$ = 11.5 and 10.3 K, respectively). At a macroscopic level, the magnetization and heat-capacity measurements under applied magnetic field provide an upper critical field of 1.93 and 0.65 T for NbC and TaC, respectively. The low-temperature superfluid density, determined by transverse-field $μ$SR and electronic specific-heat data, suggest a fully-gapped superconducting state in both NbC and TaC, with a zero-temperature gap $Δ_0 = 1.90$ and 1.45 meV, and a magnetic penetration depth $λ_0$ = 141 and 77 nm, respectively. Band-structure calculations suggest that the density of states at the Fermi level is dominated by the Nb $4d$- (or Ta $5d$-) orbitals, which are strongly hybridized with the C $p$-orbitals to produce large cylinder-like Fermi surfaces, similar to those of high-$T_c$ iron-based superconductors. Without considering the spin-orbit coupling (SOC) effect, the first Brillouin zone contains three closed node lines in the bulk band structure, protected by time-reversal and space-inversion symmetry. When considering SOC, its effects in the NbC case appear rather modest. Therefore, the node lines may be preserved in NbC, hence proposing it as a potential topological superconductor.
