Pairing symmetry in single-layer tetragonal Tl₂Ba₂CuO_6+δ superconductors

A high-resolution scanning superconducting quantum interference device microscopy study of tetragonal single-layer Tl2Ba2CuO6+δ films, deposited on tricrystal SrTiO3 substrates, demonstrates the effect of spontaneously generated half flux quanta. This observation shows that in addition to YBa2Cu3O7, the order parameter symmetry in Tl2Ba2CuO6+δ is consistent with that of a dx2-y2 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 Tl2Ba2CuO6+δ superconducting system.