Pairing Symmetry in Single-Layer Tetragonal Tl ₂ Ba ₂ CuO _β+δ Superconductors

Abstract

A high-resolution scanning superconducting quantum interference device microscopy study of tetragonal single-layer Tl 2 Ba 2 CuO 6+δ films, deposited on tricrystal SrTiO 3 substrates, demonstrates the effect of spontaneously generated half flux quanta. This observation shows that in addition to YBa 2 Cu 3 O 7 , the order parameter symmetry in Tl 2 Ba 2 CuO 6+δ is consistent with that of a d x 2 - y 2 pair state. This result also rules out any bilayer or twinning effects and any pairing that is incompatible with the fourfold rotational symmetry as in the Tl 2 Ba 2 CuO 6+δ superconducting system.