Kagome metal

In solid-state physics, the kagome metal or kagome magnet is a type of ferromagnetic quantum material. The atomic lattice in a kagome magnet has layered overlapping triangles and large hexagonal voids, akin to the kagome pattern in traditional Japanese basket-weaving.[1][2][3][4] This geometry induces a flat electronic band structure with Dirac crossings, in which the low-energy electron dynamics correlate strongly.[5]

Electrons in a kagome metal experience a "three-dimensional cousin of the quantum Hall effect": magnetic effects require electrons to flow around the kagome triangles, akin to superconductivity.[5] This phenomenon occurs in many materials at low temperatures and high external field, but, unlike superconductivity, materials are known in which the effect remains under standard conditions.[5][6]

The first room-temperature, vanishing-external-field kagome magnet discovered was the intermetallic Fe₃Sn₂, as shown in 2011.[7] Many others have since been found. Kagome magnets occur in a variety of crystal and magnetic structures, generally featuring a 3d-transition-metal kagome lattice with in-plane period ~5.5 Å. Examples include antiferromagnet Mn₃Sn, paramagnet CoSn, ferrimagnet TbMn₆Sn₆, hard ferromagnet (and Weyl semimetal) Co₃Sn₂S₂, and soft ferromagnet Fe₃Sn₂. Until 2019, all known kagome materials contained the heavy element tin, which has a strong spin–orbit coupling, but potential kagome materials under study (as of 2019) included magnetically doped Weyl-semimetal Co₂MnGa,[8] and the class AV₃Sb₅ (A = Cs, Rb, K).[9] Although most research on kagome magnets has been performed on Fe₃Sn₂, it has since been discovered that FeSn in fact exhibits a structure much closer to the ideal kagome lattice.[10]

A kagome lattice harbors massive Dirac fermions, Berry curvature, band gaps, and spin–orbit activity, all of which are conducive to the Hall Effect and zero-energy-loss electric currents.[6][11][12] These behaviors are promising for the development of technologies in quantum computing, spin superconductors, and low power electronics.[5][6]  CsV₃Sb₅ in particular exhibits numerous exotic properties, including superconductivity,[13] topological states, and more.[14][15][16][17] Magnetic skyrmionic bubbles have been found in Kagome metals over a wide temperature range. For example, they were observed in Fe₃Sn₂ at ~200-600 K using LTEM but with high critical field ~0.8 T.[18]