Dependence on the interlayer spacing of nanoscale electronic states in layered nitride chloride superconductors α-Mx TiNCl investigated by scanning tunneling microscopy/spectroscopy

Анотація

We studied the influence of interlayer spacing on the nanoscale electronic states of layered nitride chloride superconductors α-M_xTiNCl (M = pyridine (Py), Na, K) using scanning tunneling microscopy and spectroscopy. It was shown that these materials exhibit a strong decrease in the critical temperature (T_c) with increasing inter-layer spacing d. Our measurements revealed gap-like features in differential conductance spectra that remain nearly independent of T_c and d. The extracted characteristic gap energy E_g shows spatial inhomogeneity on nanometer scales and does not follow the conventional Bardeen–Cooper–Schrieffer scaling. These observations suggest that the detected gap-like feature is more consistent with pseudogap-like behavior, most probably related to other electronic properties, than with true superconducting pairing. It is similar to the situation in cuprate high-temperature superconductors, where pseudogap is a prominent feature. The results suggest the importance of the local electronic structure and doping effects in determining superconducting properties of layered systems.