Smearing origin of zero-bias conductance peak in Ag-SiO-Bi2Sr2CaCu2O8+δ planar tunnel junctions: influence of diffusive normal metal verified with the circuit theory

Abstract

Abstract. We propose a new approach of smearing origins of a zero-bias conductance peak (ZBCP) in high-Tc superconductor tunnel junctions through the analysis based on the circuit theory for a d-wave pairing symmetry. The circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP frequently appears in line shapes for this theory, in which the total resistance was constructed by taking account of the effects between a d-wave superconductor and a diffusive normal metal (DN) at a junction interface, including the midgap Andreev resonant states (MARS), the coherent Andreev reflection (CAR) and the proximity effect. Therefore, we have analyzed experimental spectra with the ZBCP of Ag-SiO-Bi2Sr2CaCu2O 8+δ (Bi-2212) planar tunnel junctions for the {110}-oriented direction by using a simplified formula of the circuit theory for d-wave superconductors. The fitting results reveal that the spectral features of the ZBCP are well explained by the circuit theory not only excluding the Dynes's broadening factor but also considering only the MARS and the DN resistance. Thus, the ZBCP behaviors are understood to be consistent with those of recent studies on the circuit theory extended to the systems containing d-wave superconductor tunnel junctions.

Transport and magnetic properties of fully-epitaxial superconducting NbN/half-metallic Heulser alloy Co2MnSi bilayer films

“…Using the fully-epitaxial NbN/Co2MnSi bilayer films, junctions for Andreev reflection measurements were made with the circular pillars in the range between 40 nm and 4 m in diameter by an electron-beam lithography technique. The differential conductance of NbN/Co2MnSi junctions was measured using a physical property measurement system (PPMS) by a conventional modulation technique 8) in the temperature range between 2K and 20 K. Table 1. The mismatch of lattice constants between a MgO(001) substrate and a NbN(001) film was improved with the decrease of nitrogen partial pressures.…”