Collapse of the Mott gap and emergence of a nodal liquid in lightly doped Sr$_2$IrO$_4$

TL;DR

This study investigates how doping affects the electronic structure of Sr$_2$IrO$_4$, revealing a collapse of the Mott gap and the emergence of nodal quasiparticles with pseudogaps, similar to underdoped cuprates, challenging existing theories.

Contribution

It provides detailed electronic structure data on doped Sr$_2$IrO$_4$, showing the collapse of the Mott gap and the formation of a nodal liquid, offering insights into Mott insulators and high-temperature superconductivity.

Findings

Rapid collapse of the Mott gap with doping.

Emergence of lens-like Fermi contours.

Presence of nodal quasiparticles with pseudogaps.

Abstract

Superconductivity in underdoped cuprates emerges from an unusual electronic state characterised by nodal quasiparticles and an antinodal pseudogap. The relation between this state and superconductivity is intensely studied but remains controversial. The discrimination between competing theoretical models is hindered by a lack of electronic structure data from related doped Mott insulators. Here we report the doping evolution of the Heisenberg antiferromagnet Sr$_2$IrO$_4$, a close analogue to underdoped cuprates. We demonstrate that metallicity emerges from a rapid collapse of the Mott gap with doping, resulting in lens-like Fermi contours rather than disconnected Fermi arcs as observed in cuprates. Intriguingly though, the emerging electron liquid shows nodal quasiparticles with an antinodal pseudogap and thus bares strong similarities with underdoped cuprates. We conclude that anisotropic pseudogaps are a generic property of two-dimensional doped Mott insulators rather than a unique hallmark of cuprate high-temperature superconductivity.