Magnetic field dependence of the density of states in the multiband superconductor β-Bi2Pd

Abstract

We present very low-temperature scanning tunneling microscopy (STM) experiments on single-crystalline samples of the superconductor β-Bi2Pd. We find a single superconducting gap from the zero-field tunneling conductance. However, the magnetic field dependence of the intervortex tunneling conductance is higher than the one expected in a single-gap superconductor. Such an increase in the intervortex tunneling conductance has been found in superconductors with multiple superconducting gaps. We also find that the hexagonal vortex lattice is locked to the square atomic lattice as expected in crystalline superconductors with anisotropic Fermi surfaces. Moreover, we compare the upper critical field Hc2(T) obtained in our sample with previous measurements and find that Hc2(T) does not increase by reducing the mean free path. We fit Hc2(T) and show that multiband Fermi surface is needed to explain the observed behavior. We propose that β-Bi2Pd is a single-gap multiband superconductor. We anticipate that single-gap superconductivity might often occur in compounds with anisotropic multiband Fermi surfaces.