Hidden Superconductivity in Solid Solutions Sr(1-x)La(x)PbO3 detected by tunneling

TL;DR

This study reports the first observation of Josephson tunneling and a superconducting gap in La-doped SrPbO3, suggesting hidden superconductivity in this family of oxides, despite the absence of bulk superconductivity.

Contribution

It provides the first evidence of superconductivity in Sr(1-x)La(x)PbO3 via tunneling measurements, revealing a superconducting gap in a previously non-superconducting family.

Findings

Sr(0.9)La(0.1)PbO3 shows a Josephson tunnel current.

Superconducting gap of approximately 10 meV detected.

No bulk superconductivity observed despite tunneling evidence.

Abstract

Solid solutions of Sr1-xLaxPbO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized with the help of high pressure. Temperature (T) dependences of the resistivity r and differential thermoelectric power S were measured. All samples demonstrate an increase of r for low T and no signs of a bulk superconducting transition. The sign of S(T) is positive for x = 0.05 and 0.10, whereas S(T) changes sign from positive to negative for x = 0.15. Tunnel measurements were carried out using the break-junction technique. The sample SrPbO3 reveals a correlation dielectric gap Sigma = 1.5 ~ 2 eV. On the other hand, Sr(0.9)La(0.1)PbO3 shows a Josephson tunnel current and a superconducting gap of approximately 10 meV. This is the first such observation for the studied family of oxides. The results may help to resolve the existing controversy over superconductivity in the conglomerates Cu24Pb2Sr2Ag2Ox.