Layered intermetallic kagomés have served as an ideal platform to study the exotic phenomenon associated with flat bands and Dirac-type dispersions. It is essential to explore the electronic properties of these structures for the experimental realization of 2D kagomé lattice in bulk materials. We explore a specific type of MT6X6 compound where M = Mg, T = Co and X = Ge. Single crystals of MgCo6Ge6 were grown by laser Bridgman technique. X-ray precession images and electron diffraction measurements collected at T = 293(2) K show that the compound crystallizes in space group P6/mmm, with a = 5.06094(15) Å, c = 7.7271(2) Å. Residual electron maps provide evidence of columnar disorder along c axis. Further investigation of the crystal structure reveals spontaneous twisting of the Co kagomé layers. We look into crystal orbital hamiltonian population analysis to understand the cooperative twisting between layers within the Co-kagomé network and the interlayer tetragonal bonding. Despite the appearance of static tilting, no evidence for a phase transition was found in magnetization, resistivity, or specific heat measurements, implying that the twisting exists at all temperatures, but is thermally fluctuating at room temperature. This behavior is further supported by looking into related materials to understand the pairwise twisting and bonding in layered structures.

Laser Bridgman growth, columnar disorder and low temperature twisting of kagomé layers in intermetallics

ACS Spring Meeting 2021

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