  High temperature superconductivity in cuprates emerges out of a highly
enigmatic `pseudogap' metal phase. The mechanism of high temperature
superconductivity is likely 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 5$d$ transition-metal oxide Sr$_2$IrO$_4$. Using
angle-resolved photoemission, we show that 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$_4$. Although the physical origin of the $d$-wave gap
remains to be understood, Sr$_2$IrO$_4$ is a 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.
