Symmetry of the superconducting order parameter in Bi2Sr2CaCu2Ox

Abstract

We analyzed the symmetry of the superconducting-phase condensate of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$ with photoemission at high energy and angular resolution. The result unambiguously demonstrates that the photohole must include non-s-wave components. Under the hypothesis of a pure d-wave symmetry, this would be identified as ${\mathit{d}}_{\mathit{x}\mathit{z}}$+${\mathit{d}}_{\mathit{y}\mathit{z}}$. Our superconducting state data are, specifically, incompatible with pure ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ symmetry. Mixed symmetries, however, cannot be excluded as long as they include a non-s-wave component. We specifically observe a change in the symmetry of electronic states between the normal state and the superconducting state.