准一维Cr基超导体RbCr3As3的超导能隙

RbCr₃As₃是具有[（Cr₃As₃）^-]_∞线性链的准一维超导体，超导转变温度约为6.6 K.对RbCr₃As₃单晶进行了电输运和极低温热输运性质的研究.低温下，拟合了RbCr₃As₃正常态电阻率随温度的变化，发现其满足费米液体行为.通过拟合超导转变温度随磁场的关系，得到RbCr₃As₃单晶的上临界场约为25.6 T.对RbCr₃As₃进行了零场下的极低温热导率测量，得到其剩余线性项为7.5 μW·K^-2·cm^-1，占正常态热导率值的24%.测量不同磁场下RbCr₃As₃的热导率，发现与单带s波超导体相比较，RbCr₃As₃剩余线性项随磁场增加相对较快.这些结果表明RbCr₃As₃单晶很可能是有节点的非常规超导体.

Superconducting gap of quasi-one-dimensional Cr-based superconductor RbCr3As3

Since the discovery of high-temperature superconductivity in cuprates, finding more unconventional superconductors and understanding their superconducting pairing mechanism has been an important theme in condensed matter physics. Recently, ternary Cr-based superconductors A₂Cr₃As₃ (A=K, Rb, Cs) and ACr₃As₃ (A=K, Rb) were reported, which own quasi-one-dimensional crystal structure, containing[(Cr₃As₃)^-]_∞ linear chains. A₂Cr₃As₃ belongs to P6m2 space group, and ACr₃As₃ crystallizes in a centrosymmetric structure with the space group P6₃/m. Many experiments, such as nuclear magnetic resonance, London penetration depth, show that A₂Cr₃As₃ is an unconventional superconductor. However, these A₂Cr₃As₃ compounds are extremely unstable in air. Here, we study the superconducting gap of the air-stable RbCr₃As₃ single crystal, using ultralow-temperature thermal conductivity measurement. The resistivity of RbCr₃As₃ single crystal shows a superconducting transition temperature T_c^zero at 6.6 K. The normal-state resistivity data from 20 K to 8 K are fitted to ρ (T)=ρ₀ + AT², which gives a residual resistivity of ρ₀=781 μΩ·cm. Then, the thermal conductivity of RbCr₃As₃ single crystal is measured at temperature down to 80 mK and in magnetic fields up to 9 T. In zero field, residual linear term κ₀/T=7.5 μW·K^-2·cm^-1 is observed, which is about 24% of its normal-state value, suggesting nodes in the superconducting gap. At low field, the κ₀/T of RbCr₃As₃ shows a relatively faster field dependence than single-gap s-wave superconductors. These results reveal that RbCr₃As₃ is likely an unconventional superconductor with superconducting gap nodes, although the exact superconducting gap symmetry and structure for this quasi-one-dimensional superconductor needs further investigation.