Andreev reflection in superconducting state of pressurized La3Ni2O7

Abstract

The discovery of superconductivity with T_c above 77 K in pressurized La₃Ni₂O₇ has stimulated enormous interest in the field of unconventional superconductivity. A recent experiment in La₂PrNi₂O₇ has shown that the superconducting volume is close to 100%. Because the superconductivity can only be achieved under high pressures, many intrinsic properties, such as the superconducting gaps, have not been measured yet. We report the Andreev reflection measurement of pressurized La₃Ni₂O₇ with the onset superconducting transition temperature at about 77 K. Our data reveal a clear peak of differential conductivity near zero bias in the tunneling spectrum; and appear also are some temperature-dependent steps that may reflect other superconducting gaps. Calculations based on the Blonder-Tinkham-Klapwijk model with multiple components can roughly fit the data, and the central peak can be fitted with a d-wave gap with a magnitude of about 9 meV, and other two s-wave gaps at about 16 and 26 meV. The latter two large gaps are determined from the enhanced steps of the differential conductivity, which may have other origins. Our results reveal possible evidence of a sign-reversal gap and multi-component features of the superconducting gaps in the nickelate 327 systems.