Eur. Phys. J. B 54, 141-149 (2006)
https://doi.org/10.1140/epjb/e2006-00440-2

Smearing origin of zero-bias conductance peak in Ag-SiO-Bi₂Sr₂CaCu₂O_8+δ planar tunnel junctions: influence of diffusive normal metal verified with the circuit theory

¹ Department of General Education, Kumamoto National College of Technology, Kumamoto, 861-1102, Japan
² Department of Applied Physics, Nagoya University, Nagoya, 464-8603, Japan
³ CREST, Japan Science and Technology Agency (JST), Nagoya, 464-8603, Japan
⁴ Department of Physics, Kumamoto University, Kumamoto, 860-8555, Japan
⁵ Department of Applied Physics, Hokkaido University, Sapporo, 060-8628, Japan

Corresponding author: ^a shigeta@sci.kagoshima-u.ac.jp

Received: 28 January 2006
Revised: 23 October 2006
Published online: 22 December 2006

Abstract

We propose a new approach of smearing origins of a zero-bias conductance peak (ZBCP) in high-T_c 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.