Superconductivity in the misfit layer compound (PbSe)1.12(NbSe2)2

Superconducting ferecrystals: turbostratically disordered atomic-scale layered (PbSe)1.14(NbSe2)n thin films

“…For ferecrystals (hexagonal in-plane unit cell) and b PbSe  =  a PbSe (square in-plane unit cell) and x is similar or higher than in MLCs. So, while the ferecrystals studied here have stacking sequences identical to the bulk misfit layered compound single crystals studied previously20212324, they have distinctly different in-plane structures and orientations between the constituent layers. In particular, the NbSe 2 layers in the ferecrystal have the same hexagonal symmetry as found in bulk NbSe 2 and presumably in exfoliated single or few layer NbSe 2 flakes.…”

“…Some NbSe 2 layers show a projection typical for a trigonal prismatic coordination of Nb by Se atoms (Fig. 1c), as found in analogous single crystalline bulk platelets, misfit layer compounds (MLCs)2021 and in bulk 2 H -NbSe 2 22. Due to the turbostratic disorder, a local octahedral coordination of the Nb atoms, as in bulk 4 H -NbSe 2 cannot be fully excluded, but projections typical for the octahedral coordination were not observed.…”

“…As shown in Fig. 3b, the in-plane residual resistivity values of the ferecrystals are 3–17 times higher than those of the MLCs2023. We attribute this to the polycrystallinity and turbostratic disorder of the ferecrystals, leading to a higher defect scattering rate at grain boundaries and the interfaces between constituent layers.…”

“…While in general for the MLCs a qualitative decrease of the in-plane resistivity with increasing n is observed, the quantitative values also deviate from this simple model2023. According to equation (2), for n  = 2 a resistivity of about 76% of the resistivity of n  = 1 is expected, however, for the MLC a stronger decrease to about 25% of the resistivity of n  = 1 is measured.…”

“…The MLCs are synthesized as single crystalline bulk platelets with a total thickness of about 10 μm–50 μm2023242526. In ferecrystals the in-plane grain size ranges from a few to several tens of nanometers, as observed in the HAADF-STEM images.…”