Revisiting the vortex-core tunnelling spectroscopy in YBa2Cu3O7-δ.

Jens Bruér,Zoran Ristić,Ivan Maggio-Aprile,Christophe Berthod,Christoph Renner,Andreas Erb,Øystein Fischer,Nathan Jenkins

doi:10.1038/ncomms11139

Abstract

The observation by scanning tunnelling spectroscopy of Abrikosov vortex cores in the high-temperature superconductor YBa2Cu3O7−δ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterized by a strong zero-bias conductance peak. Here, we present scanning tunnelling spectroscopy data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel, which contributes to the tunnelling signal in parallel with the superconducting density of states.

Highlights

The average gap is 17.2 meV with a standard deviation of 1.9 meV, corresponding to a ratio 2DSC/kBTc 1⁄4 4.34±0.5, where kB is the Boltzmann constant and Tc is the critical temperature. This gap uniformity in Y123 contrasts with the case of Bi-based cuprates, where up to 50% inhomogeneity is often observed in the gap values, even at optimal doping and for samples with sharp superconducting transitions
The good correlation between the SC peaks and sSGS/sSC and the absence of correlation between the SGS and sSGS/sSC imply that there is no correlation between the SGS and the SC peak, as we
The absence of atomic resolution prevents a positive identification of the surface layer. It does not preclude the interpretation of the tunnelling spectra in terms of intrinsic superconducting Y123 properties as the following compelling evidences show

Summary

Introduction

The average gap is 17.2 meV with a standard deviation of 1.9 meV, corresponding to a ratio 2DSC/kBTc 1⁄4 4.34±0.5, where kB is the Boltzmann constant and Tc is the critical temperature. This gap uniformity in Y123 contrasts with the case of Bi-based cuprates, where up to 50% inhomogeneity is often observed in the gap values, even at optimal doping and for samples with sharp superconducting transitions. Until now, this structure had only been clearly resolved as peaks inside the vortices[12,15]. The well-defined subgap peaks in the average spectrum show that the energy of this structure does not vary appreciably along the surface

Methods

Results

Conclusion