SPECIAL TOPIC — Recent progress on kagome metals and superconductors

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    Enhanced anomalous Hall effect in kagome magnet YbMn6Sn6 with intermediate-valence ytterbium
    Longfei Li(李龙飞), Shengwei Chi(迟晟玮), Wenlong Ma(马文龙), Kaizhen Guo(郭凯臻), Gang Xu(徐刚), and Shuang Jia(贾爽)
    Chin. Phys. B, 2024, 33 (5): 057501.   DOI: 10.1088/1674-1056/ad322d
    Abstract77)   HTML2)    PDF (1841KB)(106)      
    We report on the magnetization and anomalous Hall effect (AHE) in the high-quality single crystals of the kagome magnet YbMn$_{6}$Sn$_{6}$, where the spins of the Mn atoms in the kagome lattice order ferromagnetically and the intermediate-valence Yb atoms are nonmagnetic. The intrinsic mechanism plays a crucial role in the AHE, leading to an enhanced anomalous Hall conductivity (AHC) compared with the other rare-earth $R$Mn$_{6}$Sn$_{6}$ compounds. Our band structure calculation reveals a strong hybridization between the 4f electrons of Yb and conduction electrons.
    Superconductivity in kagome metal ThRu3Si2
    Yi Liu(刘艺), Jing Li(厉静), Wu-Zhang Yang(杨武璋), Jia-Yi Lu(卢佳依), Bo-Ya Cao(曹博雅), Hua-Xun Li(李华旬), Wan-Li Chai(柴万力), Si-Qi Wu(武思祺), Bai-Zhuo Li(李佰卓), Yun-Lei Sun(孙云蕾), Wen-He Jiao(焦文鹤), Cao Wang(王操), Xiao-Feng Xu(许晓峰), Zhi Ren(任之), and Guang-Han Cao(曹光旱)
    Chin. Phys. B, 2024, 33 (5): 057401.   DOI: 10.1088/1674-1056/ad1c5e
    Abstract64)   HTML4)    PDF (1560KB)(57)      
    We report the physical properties of ThRu$_3$Si$_2$ featured with distorted Ru kagome lattice. The combined experiments of resistivity, magnetization and specific heat reveal bulk superconductivity with $T_{\rm{c}}= 3.8$ K. The specific heat jump and calculated electron-phonon coupling indicate a moderate coupled BCS superconductor. In comparison with LaRu$_3$Si$_2$, the calculated electronic structure in ThRu$_3$Si$_2$ shows an electron-doping effect with electron filling lifted from 100 meV below flat bands to 300 meV above it. This explains the lower superconducting transition temperature and weaker electron correlations observed in ThRu$_3$Si$_2$. Our work suggests the $T_{\rm{c}}$ and electronic correlations in the kagome superconductor could have an intimate connection with the flat bands.
    Two-fold symmetry of the in-plane resistance in kagome superconductor Cs(V1-xTax)3Sb5 with enhanced superconductivity
    Zhen Zhao(赵振), Ruwen Wang(王汝文), Yuhang Zhang(张宇航), Ke Zhu(祝轲), Weiqi Yu(余维琪), Yechao Han(韩烨超), Jiali Liu(刘家利), Guojing Hu(胡国静), Hui Guo(郭辉), Xiao Lin(林晓), Xiaoli Dong(董晓莉), Hui Chen(陈辉), Haitao Yang(杨海涛), and Hong-Jun Gao(高鸿钧)
    Chin. Phys. B, 2024, 33 (7): 077406.   DOI: 10.1088/1674-1056/ad4ffa
    Abstract32)      PDF (1895KB)(75)      
    The kagome superconductor CsV$_{3}$Sb$_{5}$ has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave (CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electronic orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$ by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of $ x$ is over 0.07. Concurrently, the superconductivity is enhanced monotonically from $T_{\rm c} \sim 2.8 $ K at $x =0$ to 5.2 K at $x = 0.12$. Intriguingly, in the absence of CDW, Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$ ($x = 0.12$) crystals exhibit a pronounced two-fold symmetry of the in-plane angular-dependent magnetoresistance (AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$. Our findings demonstrate that Cs(V$_{1-x}$Ta$_{x}$)$_{3}$Sb$_{5}$ with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.