Insulating boundary layer and magnetic scattering in YBa2Cu3O7−δ /Ag interfaces over a contact resistivity range of 10−8–10−3 Ω cm2

Abstract

We have measured interface transport in thin-film YBa2Cu3O7−δ /Ag interfaces having resistivities ranging from 10−8 to 10−3 Ω cm2. Analysis of the interface I-V data indicates that tunneling is the predominant transport mechanism even for the in situ interfaces having contact resistivities of 1–7×10−8 Ω cm2. Zero-bias conductance peaks are also observed for the entire range of interface resistivity. The similarity of the zero-bias conductance peaks among these widely varying interfaces suggests that the low-temperature interface transport is governed by the same mechanism in each case. These conductance peaks are analyzed in the framework of the Appelbaum–Anderson model for tunneling assisted by magnetic scattering from isolated magnetic spins in the interface.

Conductance–voltage characteristics of interfaces between YBa2Cu3O7 and metallic oxides

“…Even when the CRO is grown at different temperatures ͑600 and 700°C͒, we observe the same conductance-voltage characteristics, suggesting that the main interface property is probably not caused by cation diffusion. 8,11 However we do not observe a minimum in the zero bias conductance as a function of temperature as reported by Sanders et al 11 SrRuO 3 , which has the same structure as that of the CRO but a slightly bigger lattice constant, undergoes ferromagnetic ordering at temperatures around 150 K. 15 The magnetic ordering in SRO is believed to be a 4d itinerant ferromagnetism with a moment of about 1.1 B per Ru atom. In addition to the Kondo-assisted tunneling, leading to the zero bias peak, the conductance of the junction can also be modified at higher bias by resonant tunneling or hopping through localized states in the barrier.…”

“…However this would be in contradiction with Sanders et al, 11 who reported a ZBCP for YBCO/Ag interface resistance varying from 10 Ϫ3 to 10 Ϫ8 ⍀ cm 2 and with Lesueur et al, 8 who observed the ZBCP in the ab direction YBCO/Pb junctions but not in the highly resistive c direction. It is not yet clear why only the YBCO/͑Ca,Sr͒RuO 3 interfaces show a ZBCP.…”

“…8 The conductance peak is explained within the Applebaum-Anderson model which describes a tunneling process across an insulating barrier containing localized magnetic moments. 11 They also reported the splitting of the conductance peak in magnetic field, as predicted by the Applebaum-Anderson model, and found a very large g factor for the magnetic moment. This process is called the Kondoassisted tunneling, by analogy with the increase of the resistance at lower temperature in alloys with localized magnetic moments.…”

Correlation betweend-wave pairing behavior and magnetic-field-dependent zero-bias conductance peak

“…1 Near zero voltage bias, a peak is evident in the G-V curves of Fig. 1, which decreases with temperature and disappears for temperatures above ϳ30 K. 2,15 The zero-bias conductance peak is nearly independent of film manufacturer, junction resistivity ͑from 10 Ϫ8 ⍀ cm 2 to 10 Ϫ3 ⍀ cm 2 ͒, 15 and the counter-electrode material ͑including noble metals such as Au, Ag, and Pt, 16 metals having a high oxygen affinity, such as Pb, Ag, Cu, In, and Al, 1,2,15 as well as metallic oxides 17 ͒. Furthermore, oxygen annealing does not significantly alter the ZBCP even though the junction conductance changes by several orders of magnitude, as shown by the inset in Fig.…”

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

“…The ZBCP that results from the Anderson-Appelbaum scattering has been studied thoroughly via previous experiments [18][19][20][21][22]. However, only until recently was there an alternate theory to explain the origin of the ZBCP.…”