Anomalous Nodal Gap in a Doped Spin-1/2 Antiferromagnetic Mott Insulator

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal an anomalous nodal gap in doped Sr₂IrO₄, paralleling phenomena in cuprates, and suggests a unified pathway to nodal metallicity in doped antiferromagnetic Mott insulators.

Contribution

It uncovers the evolution of the nodal gap in electron-doped Sr₂IrO₄, demonstrating similarities with cuprates and proposing a common mechanism for nodal metallicity in doped Mott insulators.

Findings

Anomalous nodal gap persists after AFM gap collapse.

Nodal gap decreases and vanishes into a point node with doping.

Replicates features observed in both electron- and hole-doped cuprates.

Abstract

Many emergent phenomena appear in doped Mott insulators near the insulator-to-metal transition. In high-temperature cuprate superconductors, superconductivity arises when antiferromagnetic (AFM) order is gradually suppressed by carrier doping, and a $\textit{d}$-wave superconducting gap forms when an enigmatic nodal gap evolves into a point node. Here, we examine electron-doped Sr$_{2}$IrO$_{4}$, the 5$\textit{d}$-electron counterpart of cuprates, using angle-resolved photoemission spectroscopy. At low doping levels, we observe the formation of electronic states near the Fermi level, accompanied by a gap at the AFM zone boundary, mimicking the AFM gap in electron-doped cuprates. With increasing doping, a distinct gap emerges along the (0,0)-($\pi$,$\pi$) nodal direction, paralleling that observed in hole-doped cuprates. This anomalous nodal gap persists after the collapse of the AFM gap and gradually decreases with further doping. It eventually vanishes into a point node of the reported $\textit{d}$-wave gap. These observations replicate the characteristic features in both electron- and hole-doped cuprates, indicating a unified route toward nodal metallicity in doped spin-1/2 AFM Mott insulators.