Broken particle-hole symmetry at atomically flat a-axis YBa2Cu3O7-d interfaces

TL;DR

This study reveals that atomically flat a-axis YBa2Cu3O7-d interfaces exhibit intrinsic particle-hole symmetry breaking, evidenced by asymmetric tunneling conductance, challenging previous assumptions of symmetry in high-temperature superconductors.

Contribution

It demonstrates intrinsic particle-hole symmetry breaking at atomically flat YBCO interfaces, a novel finding in high-temperature superconductor physics.

Findings

Asymmetric tunneling conductance near zero bias

Evidence of broken particle-hole symmetry over large areas

High-quality epitaxial interfaces achieved

Abstract

We have studied quasiparticle tunneling into atomically flat a-axis films of YBa2Cu3O7-d and DyBa2Cu3O7-d through epitaxial CaTiO3 barriers. The junction heterostructures were grown by oxide molecular beam epitaxy and were carefully optimized using in-situ monitoring techniques, resulting in unprecedented crystalline perfection of the superconductor/insulator interface. Below Tc, the tunneling conductance shows the evolution of a large unexpected asymmetrical feature near zero bias. This is evidence that superconducting YBCO crystals, atomically truncated along the lobe direction with a titanate layer, have intrinsically broken particle-hole symmetry over macroscopically large areas.