Tunneling spectroscopy of layered superconductors: intercalated Li0.48(C4H8O)xHfNCl and De-intercalated HfNCl0.7

Scanning-tunneling microscopy/spectroscopy and break-junction tunneling spectroscopy of FeSe1–xTex

“…In Fig. 7(b), superconducting zero-T gap versus T c plots for several iron-based superconductors are shown together with those of some copper oxides as well as of previously investigated by us layered nitrochloride superconductors [28,39]. All the measurements were done by the fixed design of BJTS.…”

“…Namely, the slope is about the s-wave BCS weak-coupling value in iron-based superconductors, while it is more than twice that in the copperoxide and nitrochloride superconductors. Therefore, it is clear that cuprates and nitrochlorides possess unusually large energy scale of the pairing interaction, the origin of which remains to be clarified [39,40]. As for cuprates, it might be a consequence of the charge-density-wave (CDW) influence on superconductivity [41].…”

Tunneling STM/STS and break-junction spectroscopy of the layered nitro-chloride superconductors MNCl (M = Ti, Hf, Zr)

“…The local Cooper pairing in nanometer regions is almost unchanged upon warming, while superconductivity in other surface regions is suppressed much stronger than what would have been expected from the mean-field temperature behaviour. This circumstance may be the origin of the unusual T-dependence of the gap values found by BJTS [5]. In figure 4, the STS conductance mapping and the averaged conductance G(V) are shown at 77 K. In the G(10mV) mapping, the conductivity is enhanced on the cation sites and this provides a good indication of the surface cleanliness even at this high temperature.…”

“…Among experimental methods of investigating such mechanisms, electron-tunneling spectroscopy is an essential technique since it directly probes the energy gap 2Δ. It seems that the huge gap previously found by us to be far above the weak-coupling BCS cannot be explained by the conventional approach [5][6][7]. In particular, the strong-coupling Migdal-Eliashberg theory fails to explain superconductivity of MNCl [4].…”

“…In particular, the strong-coupling Migdal-Eliashberg theory fails to explain superconductivity of MNCl [4]. In this paper, the superconducting gaps of α-and β-types of MNCl having different crystal structures are examined at the nanometer length scale by scanning-tunneling spectroscopy (STS) and are compared with their counterparts found from the break-junction tunneling spectroscopy (BJTS) measurements [5][6][7]. Polycrystals of MNCl were synthesized by a method reported elsewhere [1][2][3].…”