Twisting of 2D Kagomé Sheets in Layered Intermetallics

Abstract

Chemical bonding in 2D layered materials and van der Waals solids is central to understanding and harnessing their unique electronic, magnetic, optical, thermal, and superconducting properties. Here, we report the discovery of spontaneous, bidirectional, bilayer twisting (twist angle ∼4.5°) in the metallic kagomé MgCo 6 Ge 6 at T = 100(2) K via X-ray diffraction measurements, enabled by the preparation of single crystals by the Laser Bridgman method. Despite the appearance of static twisting on cooling from T ∼300 to 100 K, no evidence for a phase transition was found in physical property measurements. Combined with the presence of an Einstein phonon mode contribution in the specific heat, this implies that the twisting exists at all temperatures but is thermally fluctuating at room temperature. Crystal Orbital Hamilton Population analysis demonstrates that the cooperative twisting between layers stabilizes the Co-kagomé network when coupled to strongly bonded and rigid (Ge 2 ) dimers that connect adjacent layers. Further modeling of the displacive disorder in the crystal structure shows the presence of a second, Mg-deficient, stacking sequence. This alternative stacking sequence also exhibits interlayer twisting, but with a different pattern, consistent with the change in electron count due to the removal of Mg. Magnetization, resistivity, and low-temperature specific heat measurements are all consistent with a Pauli paramagnetic, strongly correlated metal. Our results provide crucial insight into how chemical concepts lead to interesting electronic structures and behaviors in layered materials.

Electronic Properties and Phase Transition in the Kagome Metal Yb0.5Co3Ge3

“…These are related to each other by a sixfold screw axis along c , and an inversion center is located between the Kagome nets, making the full structure centrosymmetric, even though a single distorted Kagome net breaks inversion symmetry (Figure d). The distorted Kagome net at low temperature is distinct from AV 3 Sb 5 family, , a similar distortion has been seen in the Kagome metals MgCo 6 Ge 6 , LaRu 3 Si 2 , and YRu 3 Si 2 , and some of the phases are superconductors but show no sign of magnetic or CDW transitions above T c . − It is worth noting that although a magnetic transition at low temperature (18 K) was detected in the previous magnetic susceptibility study, no magnetic transition signal was observed between 50 and 300 K . This may be related to the distortion of the Co Kagome nets, which is inverted between the two layers and may influence magnetization; future experiments such a muon spin relaxation may help to explicitly understand the magnetism and its relation to the resistive transition in Yb 0.5 Co 3 Ge 3 .…”

Structural, Thermodynamic, and Transport Properties of the Small-Gap Two-Dimensional Metal–Organic Kagomé Materials Cu3(hexaiminobenzene)2 and Ni3(hexaiminobenzene)2

“…27 Thus, we conclude that the specimens measured here are small-bandgap semiconductors. These bandgaps are much smaller than those observed in most kagoméminerals, but also far from the metallicity observed in materials such as Fe 3 Sn 2 , MgCo 6 Ge 6 , 28 and KV 3 Sb 5 , 8−10,29 and place Ni 3 (HIB) 2 and Cu 3 (HIB) 2 much farther from the insulating limit than most QSL candidates. It is also interesting to compare our Ni 3 (HIB) 2 and Cu 3 (HIB) 2 results to those of other recently discovered kagoméMOFs.…”

Optimization of PbTiO3 Single Crystals with Flux and Laser Floating Zone Method

“…Works reporting using a floating zone furnace for PbTiO 3 had very fast growth speeds (100 mm/h) and were largely unsuccessful due to the evaporation of PbO leading to an unstable, collapsing zone . Recent progress in the use of laser diode floating zone (LDFZ) furnaces in synthesizing a wide variety of materials, − including those with high vapor pressures, − encourages revisitation of this technique as applied to PbTiO 3 . Here we report the growth of bulk crystals (4 cm length, ∼5 mm OD) of PbTiO 3 using the LDFZ.…”