Comment on ‘‘Valence-band states inBi2(Ca,Sr,La)3Cu2O8’’

In a recent paper, Wells et al. conclude from angle-resolved photoemission spectroscopy that the electronic states at the Fermi energy (${\mathit{E}}_{\mathit{F}}$) of ${\mathrm{Bi}}_2$(Ca,Sr,La${)}_3$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_8$ have mainly O 2${\mathit{p}}_{\mathit{x}}$ and 2${\mathit{p}}_{\mathit{y}}$ symmetry, while O ${2\mathrm{p}}_{\mathrm{z}}$-like states are not permitted by symmetry at ${\mathit{E}}_{\mathit{F}}$. I point out here a deficiency in Wells’ et al. symmetry analysis which, when corrected, allows for a significant O 2${\mathit{p}}_{\mathit{z}}$ contribution at ${\mathit{E}}_{\mathit{F}}$. The resultant degenerate O${\mathit{p}}_{\mathit{z}}$–O${\mathit{p}}_{\mathit{z}}$ ‘‘resonant π bonds’’ at ${\mathit{E}}_{\mathit{F}}$ parallel to the Cu-O a-b planes, promoted by significant Cu ${\mathrm{d}}_{\mathrm{x}\mathrm{z},}$yz–O${\mathit{p}}_{\mathit{z}}$ ${\mathrm{\pi }}^{\mathrm{*}}$-antibonding hybridization, along with their associated shallow ‘‘double-well’’ potentials, are the basis for a dynamic Jahn-Teller mechanism of high-${\mathit{T}}_{\mathit{c}}$ superconductivity in cuprates.