[Paper Review] Discovery of a quantum limit Chern magnet TbMn6Sn6

Jia‐Xin Yin, Wenlong Ma+24 more|arXiv (Cornell University)|Jun 8, 2020

Topological Materials and Phenomena38 references35 citations

TL;DR

The paper reports discovery of a topological kagome magnet TbMn6Sn6 showing Landau quantization, spin-polarized Dirac dispersion with a large Chern gap, and bulk–edge–Berry correspondence indicative of a quantum-limit Chern phase.

ABSTRACT

The quantum level interplay between geometry, topology, and correlation is at the forefront of fundamental physics. Owing to the unusual lattice geometry and breaking of time-reversal symmetry, kagome magnets are predicted to support intrinsic Chern quantum phases. However, quantum materials hosting ideal spin-orbit coupled kagome lattices with strong out-of-plane magnetization have been lacking. Here we use scanning tunneling microscopy to discover a new topological kagome magnet TbMn6Sn6, which is close to satisfying the above criteria. We visualize its effectively defect-free purely Mn-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state exhibits distinct Landau quantization upon the application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk-boundary correspondence between the Chern gap and topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn6Sn6, opening up an avenue for discovering topological quantum phenomena in the RMn6Sn6 (R = rare earth element) family with a variety of magnetic structures. Our visualization of the magnetic bulk-boundary-Berry correspondence covering real and momentum space demonstrates a proof-of-principle method revealing topological magnets.

Motivation & Objective

• Motivate the search for intrinsic Chern quantum phases in kagome magnets with out-of-plane magnetization.
• Demonstrate a defect-free Mn-based kagome lattice suitable for topological phenomena.
• Visualize Landau quantization and spin-polarized Dirac dispersion under magnetic field.
• Establish bulk–boundary–Berry curvature correspondences for a Chern-gapped Dirac system.
• Suggest TbMn6Sn6 as a platform to explore topological magnetism in RMn6Sn6 family.

Proposed method

• Use scanning tunneling microscopy to image the Mn-based kagome lattice at atomic resolution.
• Apply magnetic field to induce Landau quantization and observe quantized Landau fan structures.
• Identify spin-polarized Dirac dispersion and determine the Chern gap.
• Correlate bulk properties with edge states and Berry curvature to demonstrate bulk-boundary-Berry correspondence.

Experimental results

Research questions

• RQ1 Can TbMn6Sn6 realize a quantum-limit Chern phase with intrinsic kagome magnetism?
• RQ2 Does TbMn6Sn6 exhibit Landau quantization and a topologically nontrivial Chern gap under magnetic field?
• RQ3 Is there a demonstrable bulk–boundary–Berry curvature correspondence for Chern-gapped Dirac fermions in this material?
• RQ4 How does the RMn6Sn6 family behave with varying rare-earth elements in hosting topological magnetic states?

Key findings

• TbMn6Sn6 hosts a purely Mn-based ferromagnetic kagome lattice suitable for topological studies.
• Electronic states show Landau quantization under an applied magnetic field.
• The Landau fan structure is associated with spin-polarized Dirac dispersion and a sizable Chern gap.
• Evidence for bulk-boundary correspondence between the Chern gap and topological edge states.
• Berry curvature features accompany the Chern-gapped Dirac fermions, supporting a quantum-limit Chern phase in this material.