Electronic Properties and Phase Transition in the Kagome Metal Yb_0.5Co₃Ge₃

Abstract

The Kagome lattice is an important fundamental structure in condensed matter physics for investigating the interplay of electron correlation, topology, and frustrated magnetism. Recent work on Kagome metals in the AV 3 Sb 5 (A = K, Rb, and Cs) family has shown a multitude of correlation-driven distortions, including symmetry breaking charge density waves and nematic superconductivity at low temperatures. Here, we study the new Kagome metal Yb 0.5 Co 3 Ge 3 and find a temperature-dependent kink in the resistivity that is highly similar to the AV 3 Sb 5 behavior and is commensurate with an in-plane structural distortion of the Co Kagome lattice along with a doubling of the c-axis. The symmetry is lower below the transition temperature, with a breaking the in-plane mirror planes and C 6 rotation, while gaining a screw axis along the c-direction. At very low temperatures, anisotropic negative magnetoresistance is observed, which may be related to anisotropic magnetism. This raises questions about the types of the distortions in Kagome nets and their resulting physical properties including superconductivity and magnetism.

Crystal Growth and Physical Properties of Hybrid CoSn–YCo6Ge6 Structure Type LnxCo3(Ge1–ySny)3 (Ln = Y, Gd)

“…However, magnetization for H//c (the easy axis) shows a saturation moment of ∼1 μ B at 2 K. Recently, the presence of a kink at T ∼ 95 K in the electrical resistivity, coupled with a structural phase transition involving a change in space group from P6/mmm to P6 3 /m, was also found in Yb 0.5 Co 3 Ge 3 . 18 The combined structural phase transition and kink in the resistivity are characteristic of charge density waves in kagome metals, similar to what is seen for FeGe 19 and AV 3 Sb 5 . 20 The structural distortion in Yb 0.5 Co 3 Ge 3 is similar to the twisting of the equilateral triangles observed in MgCo 6 Ge 6 with the kagome nets maintaining planarity.…”

“…For single crystals, the effective magnetic moment of μ eff = 4.23 μ B is less than the spin-only moment of Yb 3+ (4.54 μ B ). However, magnetization for H// c (the easy axis) shows a saturation moment of ∼1 μ B at 2 K. Recently, the presence of a kink at T ∼ 95 K in the electrical resistivity, coupled with a structural phase transition involving a change in space group from P 6/ mmm to P 6 3 / m , was also found in Yb 0.5 Co 3 Ge 3 . The combined structural phase transition and kink in the resistivity are characteristic of charge density waves in kagome metals, similar to what is seen for FeGe and AV 3 Sb 5 .…”

“…A linear fit at the low temperatures of Y x Co 3 (Ge 1– y Sn y ) 3 ( x = 0.33, y = 0.11) T vs T 2 (Figure c) yielded γ = 9 mJ/mol K 2 and β = 0.26 mJ/mol K 4 , consistent with the results from the integral Debye fit. In the heat capacity of Y x Co 3 (Ge 1– y Sn y ) 3 , there also is a weak kink at T ∼ 118 K, possibly representing a phase transition that is reminiscent of what is seen in MgCo 6 Ge 6 and Yb 0.5 Co 3 Ge 3 . , For those compounds, kinks are also seen in the resistivity and have been shown to be related to a structural phase transition. However, for Y x Co 3 (Ge 1– y Sn y ) 3 ( x = 0.33, y = 0.11), low-temperature single-crystal X-ray diffraction data were collected down to 90 K and provided no indication of a phase transition (Tables S3 and S4).…”

“…Recently, we discovered a new hybrid structure of the CoSn and YCo 6 Ge 6 structure types Yb 0.5 Co 3 Ge 3 . , Unusual magnetic anisotropy is observed at low temperatures for Yb 0.5 Co 3 Ge 3 , where the magnetic susceptibility for H// c exhibits a noticeable increase near 20 K, while a similar feature is not observed when measured along H// a and is proposed to be an indication of spin canting or reorientation . For single crystals, the effective magnetic moment of μ eff = 4.23 μ B is less than the spin-only moment of Yb 3+ (4.54 μ B ).…”

Tiny Sc Allows the Chains to Rattle: Impact of Lu and Y Doping on the Charge-Density Wave in ScV6Sn6

“…Kagome metals have recently attracted significant interest for their unusual electronic and magnetic properties arising from kagome sheets of transition metals. − A growing number of these materials display a CDW at low temperatures, especially when vanadium forms the kagome net. The AV 3 Sb 5 materials (A = K, Rb, Cs) host both superconductivity and curious CDW phases. − ,− V 3 Sb 2 likely has a CDW transition as well …”