[Paper Review] Quantum states and intertwining phases in kagome materials

Yaojia Wang, Heng Wu+3 more|arXiv (Cornell University)|Mar 6, 2023

Advanced Condensed Matter Physics160 references4 citations

TL;DR

This review explores the interplay of topology, electron correlations, and magnetism in kagome materials, highlighting emergent quantum phases such as intertwined charge order and superconductivity in kagome metals, modulated magnetism and topology in kagome magnets, and symmetry breaking with Mott physics in breathing kagome insulators. The key contribution is a comprehensive synthesis of current experimental and theoretical advances, identifying open questions and future directions in this rapidly evolving field of quantum materials.

ABSTRACT

In solid materials, nontrivial topological states, electron correlations, and magnetism are central ingredients for realizing quantum properties, including unconventional superconductivity, charge and spin density waves, and quantum spin liquids. The Kagome lattice, made up of connected triangles and hexagons, can host these three ingredients simultaneously and has proven to be a fertile platform for studying diverse quantum phenomena including those stemming from the interplay of these ingredients. In this review, we introduce the fundamental properties of the Kagome lattice as well as discuss the complex observed phenomena seen in several emergent material systems such as the intertwining of charge order and superconductivity in some Kagome metals, modulation of magnetism and topology in some Kagome magnets, and symmetry breaking with Mott physics in the breathing Kagome insulators. We also highlight many open questions in the field as well as future research directions of Kagome systems.

Motivation & Objective

• To synthesize recent experimental and theoretical advances in kagome materials that host nontrivial topological states, electron correlations, and magnetism.
• To elucidate the complex interplay between topology, correlation effects, and magnetic order in kagome lattice systems.
• To identify and highlight open questions and future research directions in kagome quantum materials.
• To examine the emergence of intertwined quantum phases such as coexisting charge density waves and superconductivity in kagome metals.
• To analyze symmetry-breaking phenomena and Mott physics in breathing kagome insulators through a unified framework.

Proposed method

• Systematic review of experimental and theoretical studies on kagome materials across multiple material classes: kagome metals, kagome magnets, and breathing kagome insulators.
• Analysis of quantum phenomena using concepts from topological quantum matter, strongly correlated electron systems, and symmetry-protected phases.
• Use of group theory and symmetry analysis to understand the emergence of broken-symmetry states and topological invariants in kagome lattices.
• Integration of data from angle-resolved photoemission spectroscopy (ARPES), quantum transport, and neutron scattering to characterize electronic and magnetic order.
• Application of effective Hamiltonians and mean-field theories to model intertwined phases such as spin and charge density waves.
• Comparison of different kagome systems to identify universal principles governing quantum phase competition and coexistence.

Experimental results

Research questions

• RQ1 How do topology, electron correlations, and magnetism coexist and influence one another in kagome materials?
• RQ2 What mechanisms drive the coexistence and competition between charge order and superconductivity in kagome metals?
• RQ3 How does magnetic order modulate topological properties in kagome magnets?
• RQ4 What role does lattice distortion (breathing distortion) play in stabilizing Mott insulating states in kagome systems?
• RQ5 What are the key open questions and future research directions in the study of quantum phases in kagome materials?

Key findings

• Kagome materials host a rich interplay of nontrivial topology, electron correlations, and magnetism, enabling the emergence of unconventional quantum phases.
• Intertwined charge order and superconductivity have been observed in kagome metals such as AV3Sb5, indicating strong competition and coexistence of broken-symmetry states.
• In kagome magnets, magnetic order can hybridize with topological band structures, leading to tunable topological states and potential for topological magnetoelectric effects.
• Breathing kagome insulators exhibit symmetry-breaking Mott physics, where lattice distortions lift degeneracies and stabilize Mott insulating ground states.
• Theoretical models suggest that spin-charge separation and fractionalized excitations may emerge in kagome systems under strong correlations, pointing to possible quantum spin liquid behavior.
• Despite progress, the precise nature of the ground states in many kagome materials remains unresolved, with competing orders and quantum criticality posing key challenges.