Fermi Arcs in a Doped Pseudospin-1/2 Heisenberg Antiferromagnet

Abstract: High temperature superconductivity in cuprates arises from an electronic state that remains poorly understood. We report the observation of a related electronic state in a non-cuprate material Sr2IrO4 in which the unique cuprate Fermiology is largely reproduced. Upon surface electron doping through in situ deposition of alkali-metal atoms, angle-resolved photoemission spectra of Sr2IrO4 display disconnected segments of zero-energy states, known as Fermi arcs, and a gap as large as 80 meV. Its evolution toward a normal metal phase with a closed Fermi surface as a function of doping and temperature parallels that in the cuprates. Our result suggests that Sr2IrO4 is a useful model system for comparison to the cuprates.

• The paper demonstrates that doping Sr₂IrO₄ produces Fermi arcs and a metal-insulator transition analogous to pseudogap behavior in cuprates.
• It utilizes ARPES and in situ alkali metal deposition to track gap evolution up to 80 meV and the transition from disconnected arcs to a closed Fermi surface.
• The findings position Sr₂IrO₄ as a promising analog for studying high-temperature superconductivity and revealing correlated electron phenomena.

Analysis of Fermi Arcs in Sr$_2$IrO$_4$: Insights from a Novel Antiferromagnetic System

The paper explores the electronic properties of Sr$_2$IrO$_4$, an antiferromagnetic Mott insulator, investigating its potential as a model system analogous to high-temperature superconducting cuprates. A notable emphasis is placed on the observation of Fermi arcs within this non-cuprate material, a phenomenon predominantly associated with the enigmatic pseudogap state in cuprates. The investigation is situated at the intersection of strong spin-orbit coupling and Heisenberg antiferromagnetic interactions present in a pseudo-spin-1/2 system, drawing parallels to cuprate Fermiology.

Key Findings

Upon surface electronic doping facilitated by the in situ deposition of alkali metal atoms, Angle-Resolved Photoemission Spectroscopy (ARPES) reveals that Sr$_2$IrO$_4$ exhibits distinct slices of zero-energy states, analogous to Fermi arcs, with a gap reaching up to 80 meV. This study outlines the transition of Sr$_2$IrO$_4$ from a Mott-insulating state to a more conventional metallic phase as doping levels and temperatures increase, mirroring similar transitions observed in cuprates.

The research highlights two pivotal observations:

1. As surface coverage by potassium atoms changes from 0.5 ML to 1 ML, marking the doping evolution, a crossover from disconnected Fermi arcs to a large, closed Fermi surface is noted, signifying a metal-insulator transition.
2. The antinodal gap prominently observed at lower dopings and temperatures diminishes and eventually disappears at higher doping levels or temperatures, adhering to some attributes of the pseudogap in cuprates.

Implications

The study proposes that the presence of Fermi arcs signifies an essential characteristic of systems akin to the cuprates, potentially underscoring a fundamental aspect of high-temperature superconductivity (HTSC). This realization positions Sr$_2$IrO$_4$ as a promising analog to study unconventional superconductivity, offering insights into HTSC mechanisms and electronic phenomena such as the pseudogap.

This work further broadens the theoretical understanding of Mott physics intertwined with strong correlations in partially filled t$_{2g}$ shells under moderate-to-strong electron interactions, typical for materials with spin-orbit coupling similar to Sr$_2$IrO$_4$. In consolidation with previously observed phenomena in cuprates, the findings suggest that Fermi arcs may symbolize a more generalized feature of doped Mott insulators rather than being peculiar to copper oxides alone.

Future Directions

The research opens several trajectories for future exploration. It beckons further experimental scrutiny into competing phases in Sr$_2$IrO$_4$, analogous to the stripe or density wave orders detected in cuprates, to ascertain commonalities which might underpin HTSC. Moreover, discerning whether these Fermi arcs foreshadow d-wave superconductivity formation could significantly advance our conception of superconducting states in doped Mott insulators.

Additionally, detailed investigations into the temperature and doping-dependent dynamics of the gap, alongside a more refined quantification of the electron doping inconsistencies, are imperative for a comprehensive understanding of the unconventional metallic states observed.

In conclusion, by demonstrating that Sr$_2$IrO$_4$ emulates key electronic behaviors of cuprates, this study enriches the dialogue on HTSC and underscores the material's utility in elucidating complex quantum phenomena inherent to strongly correlated electron systems. The insights procured could pave avenues for the synthesis and characterization of new materials exhibiting unconventional superconductivity, potentially informing the development of energy-efficient technologies predicated upon high-temperature superconductivity.