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Topological kagome magnets and superconductors (2212.11628v1)

Published 22 Dec 2022 in cond-mat.str-el and cond-mat.supr-con

Abstract: A kagome lattice naturally features Dirac fermions, flat bands and van Hove singularities in its electronic structure. The Dirac fermions encode topology, flat bands favour correlated phenomena such as magnetism, and van Hove singularities can lead to instabilities towards long-range many-body orders, altogether allowing for the realization and discovery of a series of topological kagome magnets and superconductors with exotic properties. Recent progress in exploring kagome materials has revealed rich emergent phenomena resulting from the quantum interactions between geometry, topology, spin and correlation. Here we review these key developments in this field, starting from the fundamental concepts of a kagome lattice, to the realizations of Chern and Weyl topological magnetism, to various flat-band many-body correlations, and then to the puzzles of unconventional charge-density waves and superconductivity. We highlight the connection between theoretical ideas and experimental observations, and the bond between quantum interactions within kagome magnets and kagome superconductors, as well as their relation to the concepts in topological insulators, topological superconductors, Weyl semimetals and high-temperature superconductors. These developments broadly bridge topological quantum physics and correlated many-body physics in a wide range of bulk materials and substantially advance the frontier of topological quantum matter.

Citations (187)

Summary

An Analysis of Topological Kagome Magnets and Superconductors

The exploration of kagome lattice structures has introduced pivotal developments in the research of quantum materials, particularly in the realms of magnetism and superconductivity. The paper by Jia-Xin Yin, Biao Lian, and M. Zahid Hasan provides an exhaustive review of these advancements, detailing the interplay between geometry, topology, and electronic correlations in kagome materials. Kagome lattices, characterized by their unique arrangement of corner-sharing triangles, have exhibited intriguing electronic properties including Dirac fermions, van Hove singularities, and flat bands, which collectively prompt the emergence of remarkable many-body phenomena.

The kagome lattice's inherent features foster an environment conducive to the emergence of flat bands, Dirac cones, and van Hove singularities — elements crucial for understanding its electronic properties. The flat bands are particularly significant due to their potential to host correlated electronic states such as ferromagnetism and fractional Chern insulator phases. The presence of Dirac cones also introduces topologically insulating behaviors, while van Hove singularities bring about long-range order instabilities. These singularities enable the potential for unconventional orders, including charge-density waves and superconductivity.

Theoretical and Experimental Developments

The theoretical framework developed around kagome lattice systems has been continually reinforced by experimental discoveries, establishing a strong linkage between theoretical models and empirical evidence. Chern and Weyl topological phases have been realized, propelling the understanding of kagome materials further. Specifically, the investigation into Chern quantum phases finds robust representation in TbMn6_6Sn6_6 and similar materials, where spin-orbit coupling and out-of-plane magnetism culminate in measurable topological phenomena.

Moreover, Weyl fermions surface prominently in the context of antiferromagnetic spintronics within kagome materials. The 3D momentum space interactions in Mn3_3X and Co3_3Sn2_2S2_2 directly showcase the intricate interplay of these quasi-particles, which act as sources and sinks of Berry curvature, giving rise to topological Fermi arc surface states.

Kagome materials' interaction-driven topologies have sparked considerable interest, given their capacity to open topological gaps directly at the Fermi level through interaction-induced mechanisms, independent of Dirac fermion contributions. These concepts of interaction-driven topology link closely with flat band physics, providing fertile ground for the formulation and exploration of many-body phenomena.

Implications and Future Directions

The implications of these discoveries extend to both practical applications and theoretical explorations. The potential for new electronic states and the controllability of topological properties by external stimuli (e.g., magnetic fields, pressure, and chemical doping) present avenues for developing novel electronic devices. In particular, the magnetization direction control of quantum state topology in kagome materials is a testament to their comprehensive tunability.

Looking to future directions, the paper suggests several promising avenues — including the engineering of monolayer kagome magnets for clearer band structures and progress towards high-temperature fractional Chern insulator phases. Moreover, the realization of Kagome lattice arrangements in Moiré systems introduces a new dimension of tunability, potentially leading to the observation of analogous behaviors to those found in other 2D materials like twisted bilayer graphene.

In conclusion, the exploration and understanding of kagome lattice systems have dramatically enhanced the field of topological quantum materials, establishing a foundation for future innovations in both theoretical research and applied physics. The intricate interplay of topological features and strong electronic correlations within kagome materials presents ongoing challenges and opportunities integral to advancing both fundamental and applied quantum sciences.