Scanning tunneling microscopy identification of van Hove singularities and negative thermal expansion in highly oriented pyrolytic graphite with hexagonal moiré superlattices

We report a novel investigation on the structural, electronic and magnetic properties of highly-oriented-pyrolytic-graphite (HOPG) by employing STM/S, TEM SQUID. Van Hove singularities (vHs) were identified STS-acquisition local-density-of-states spectra (LDOS) acquired from moiré-superlattice-periodicities D ~0.5 nm (θ rot ~28.6°), ~2 ~7.08°) ~ 4 ~3.6°). A possible interlayer-coupling- or moiré-thickness-induced variation vHs-separation-parameter was identified. Investigation spatial-distribution moiré-superlattices exfoliation revealed also ~13.87 ~1.02°), ~13.0 ~1.09°), ~12.65 ~1.12°) ~2.03 ~7.0°). These observations further supported additional LDOS HOPG ~8 ~1.8°). In latter, unusual presence four vHs peaks evidenced existence multiple rotational effects between internal sublattices. Extended analyses performed T-XRD 12 K to 298 K. Unknown peak-features exhibiting T-dependent shifts analysed at 2θ 21° (Fig. 6A-C) 43° 6D). ZFC FC-signals exfoliated lamellae an anisotropic ferromagnetic behaviour, possibly involving coexistence (1) disorder induced percolative ferromagnetism (2) components arising locally twisted sublattices, which found exhibit moiré superlattices.