Spectroscopic evidence of the existence of substantialCa 3dderived states at the Fermi level in the Ca-intercalated graphite superconductorCaC6

Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

“…Li atoms seem to have been completely replaced by Ca and K atoms during the sample preparation. These results are consistent with the previous conclusion78 that Li metal is removed from the graphite after Ca or K intercalation. Because the EDX result indicated the existence of Ca atoms in the bulk, two scenarios can be suggested: (1) Ca was removed from the surface after cleavage of the (Ca, K)C 8 lump and (2) a region without Ca was cleaved.…”

“…Various graphite intercalation compound (GIC) superconductors have been developed using liquid-metal-alloy (LMA) and vapour-transport (VT) methods12345678910111213. The highest value of the superconducting transition temperature, T c , for the GIC superconductors at ambient pressure is currently 11.5 K for CaC 6 67.…”

“…The highest value of the superconducting transition temperature, T c , for the GIC superconductors at ambient pressure is currently 11.5 K for CaC 6 67. The strong electron-phonon coupling between the electronic state at the interlayer Ca atoms and vertical graphite vibration has been regarded as the origin of this high T c 8. Most GIC superconductors have been shown to exhibit increased T c under applied pressure9101112.…”

Superconductivity in the Honeycomb-Lattice Pnictide SrPtAs

“…MgB 2 (T c ¼ 39 K) 7) with an AlB 2 -type structure, CaAlSi (T c ¼ 5:68{7:7 K) 8,9) with an AlB 2 derivative structure, and CaC 6 (T c ¼ 11:5 K) 10,11) with an intercalated-graphite structure exhibit superconductivity with a relatively high T c owing to a strong electron-phonon coupling, 9,12,13) soft phonons, 14,15) multibands/multigaps, 16) and interlayer bands. 17) In this paper, we report superconductivity in SrPtAs with T c ¼ 2:4 K. To our knowledge, this is the first superconducting pnictide with a honeycomb lattice structure. SrPtAs crystallizes in a hexagonal KZnAs-type structure with the space group P6 3 =mmc (#194).…”

Nature of empty states in superconducting CaC6and related Li-Ca ternary graphite intercalation compounds using polarized x-ray absorption near-edge structure at the CaKedge

“…The measured T c of CaC 6 is equal to 11.5 K, i.e., two orders of magnitude greater than that of the previous record in these quasi-two-dimensional compounds (KC 8 , T c = 0.14 K). 3 For CaC 6 , the literature reports band-structure and electron-phonon coupling calculations, 4 angular-dependent magnetoresistance measurements, 5 temperature-dependent resistivity 6 and specific-heat 7 measurements, tunneling spectroscopy, 8,9 soft x-ray photoemission, 10 angle-resolved photoemission spectroscopy, 11,12 neutron scattering, 13 inelastic x-ray scattering. [14][15][16] Until 2005, the conventional picture of superconductivity in GICs relied on the electron doping of the graphene sheets: a high charge transfer from intercalant sheet to graphene was said to favor the superconductivity.…”