Observation of a d-wave gap in electron-doped Sr 2 IrO 4

High-temperature superconductivity in cuprates emerges out of a highly enigmatic pseudogap'metal phase. The mechanism of high-temperature superconductivity is probably encrypted in the elusive relationship between the two phases, which spectroscopically is manifested as Fermi arcs - disconnected segments of zero-energy states - collapsing into d-wave point nodes upon entering the superconducting phase. Here, we reproduce this distinct cuprate phenomenology in the 5d transition-metal oxide Sr 2 IrO 4 . Using angle-resolved photoemission, we show that the clean, low-temperature phase of 6-8% electron-doped Sr 2 IrO 4 has gapless excitations only at four isolated points in the Brillouin zone, with a predominant d-wave symmetry of the gap. Our work thus establishes a connection between the low-temperature d-wave instability and the previously reported high-temperature Fermi arcs in electron-doped Sr 2 IrO 4 (ref.). Although the physical origin of the d-wave gap remains to be understood, Sr 2 IrO 4 is the first non-cuprate material to spectroscopically reproduce the complete phenomenology of the cuprates, thus offering a new material platform to investigate the relationship between the pseudogap and the d-wave gap