Ultra-thin Kagome materials

epitaxially grown films fabricated with single layer precision

By leveraging their distinctive properties, we aim to develop materials that can transform technologies such as qunatum computing and spintronics.

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What Happens When Electrons Get Trapped in a Japanese Basket Weave?

What happens when you arrange atoms into a pattern of corner-sharing triangles? You get the Kagome lattice—a quantum playground hosting flat bands and graphene-like Dirac bands. From hosting dissipationless edge states via spin-orbit coupling to morphing into 3D Weyl semimetals, these magnetic materials mimic Landau levels without external fields, unlocking the future of topological quantum computing.

Our workflow

1. Fabrication

Using Molecular Beam Epitaxy (MBE) to deposit atoms layer-by-layer in ultra-high vaccuum (1e-10 mbar) to precisely fabricate atomically-thin layered materials.

2. In-situ RHEED and LEED

RHEED and LEED  for surface-sensitive diffraction measurements to determine crystal structure and geometry, performed in-situ.

3. XPS studies

Determine stoichiometric ratios using lab and synchrotron-based XPS, alongside exposure studies to analyse material composition and chemical stability.

4. AFM surface characterisation

We characterise surface topography using AFM at the Melbourne Centre for Nanofabrication and measure surface roughness.

5. ARPES

Using ARPES, we map electronic band structures to directly to reveal critical features such as flat bands and Dirac points.

6. STM and STS

Imaging nanoscale surface topology using STM and performing spectroscopy to directly probe the local density of states.

What we've discovered

Read our papers here
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ACS Nano

Reactivity of Ultrathin Kagome Metal FeSn toward Oxygen and Water

The kagome metal FeSn alternates iron kagome layers, offering great potential for low-energy spintronics. Using synchrotron X-ray photoelectron spectroscopy and DFT calculations, we studied the air stability of epitaxial films under 10 nm thick. Atmospheric and controlled in situ oxygen & water exposures reveal highly selective oxidation: it occurs almost exclusively within the tin honeycomb Sn2 layers, forming a stable 3 nm oxide within 10 minutes. Crucially, the iron kagome layers remain pristine, preserving the material's metallic Dirac bands. This unique self-passivating behaviour provides a new blueprint for engineering future kagome-based quantum devices.

September 26, 2024
Nanoscale Horizons

CoX2Y4: a family of two-dimensional magnets with versatile magnetic order

We predict diverse magnetic orders in 2D single septuple layers of CoX2Y4. Driven by 90-degree Co-Te(Se)-Co superexchange, all show antiferromagnetism (AFM). CoBi2Te4 presents unique non-collinear AFM due to competing interactions on its triangular lattice and a tiny J2/J1 ratio. Applying strain can tune CoSb2Te4 from collinear to non-collinear AFM, offering a promising platform for nanoscale spintronics.

August 7, 2024
Nanoscale

MnBi2Te4 epitaxial thin films as a platform for realising QAHE

Since 2013, magnetic disorder has limited the quantum anomalous Hall effect (QAHE) to temperatures below 1 K. Intrinsic MnBi2Te4 should improve this, but molecular beam epitaxy (MBE) thin films fail to exhibit zero-field QAHE. This mini-review discusses why defects and magnetic disorder cause this breakdown, proposing strategies to achieve higher-temperature QAHE devices.

July 2, 2024
Journal of Physics: Materials

2024 roadmap on 2D topological insulators

2D topological insulators offer 1D spin-momentum locked edge states around an insulating bulk, promising revolutionary spintronic and quantum devices. Sizable bulk energy gaps now allow for potential room-temperature applications. Combining them into heterostructures with functional materials extends their utility, whilst electrical control could induce phase transitions or superconducting pairing for fault-tolerant quantum computing.

March 5, 2024
Phys. Rev. B

Floquet engineering in the presence of optically excited carriers

Floquet engineering optically manipulates electronic band structures, but pump-excited carriers cause heating that obscures measurements. Using multidimensional coherent spectroscopy on monolayer WS2, we measure exciton coherence during Floquet pump pulses. Coherence amplitude quantifies broadening from two-photon absorption, whilst average phase evolution tracks instantaneous band structure changes independently, effectively isolating heating from coherent band engineering.

March 4, 2024
Advanced Materials

Topological Protection in Magnetic Topological Insulator MnBi2Te4

Quantum anomalous Hall (QAH) insulators feature lossless charge transport along chiral edge states, but this topological protection often breaks down below the magnetic ordering temperature. Using scanning tunnelling microscopy on five-layer MnBi2Te4, we map the magnetic exchange gap and observe large spatial fluctuations. The gapless bulk regions hybridise with the edge states, destroying protection. Applying a small magnetic field restores the gap, proving magnetic disorder limits higher-temperature QAH effects.

February 24, 2024
Frontiers in Nanotechnology

AA-stacked bilayer graphene

We studied quasi-freestanding bilayer graphene on silicon carbide intercalated by calcium using LEED, ARPES, and DFT. Calcium intercalates strictly at the graphene-SiC interface, displacing hydrogen and inducing high n-doping. ARPES and DFT reveal that the band dispersion deviates from typical Bernal (AB) stacking, instead matching AA-stacked bilayer graphene, indicating a spontaneous stacking transition upon intercalation.

February 5, 2024
Chinese Physics B

Magnetic and electronic properties of bulk and two-dimensional FeBi2Te4

We investigated the magnetic and electronic properties of FeBi2Te4. Unlike its counterpart MnBi2Te4, bulk and few-layer FeBi2Te4 favor a 120-degree noncollinear antiferromagnetic ground state and are topologically trivial narrow-gap semiconductors. However, applying a magnetic field to the bilayer form induces a ferromagnetic state that hosts a quantum anomalous Hall effect, offering a platform to study magnetic frustration.

August 1, 2023
ACS Nano

Coherent Exciton Dynamics in Monolayer WS2

Floquet engineering offers optical control of quantum systems, but switching driving fields introduces nonadiabaticity. Using multidimensional coherent spectroscopy on monolayer WS2, we measure valley exciton phase rotations exceeding pi during a 100 fs pump pulse, driven by AC-Stark and Bloch-Siegert shifts. While the phase smoothly follows the pulse envelope, power broadening introduces extra decoherence, highlighting limitations for qubit manipulation.

July 26, 2023
Physics. Rev. Materials

Increased phase coherence length in a porous topological insulator

We increased the surface area of Bi2Te3 thin films by introducing nanoscale porosity. Resistivity measurements showed the porous samples became more metallic, confirming surface-dominated transport. Weak antilocalization was observed, with the phase coherence length doubling in porous films due to the large Fermi velocity of the Dirac surface states. Nanoporosity enhances, rather than destroys, these topological states.

June 15, 2023
Phys. Rev. B

Antiferromagnetic topological insulating state

Topological insulators feature insulating bulks and protected surface states, enabling quantized anomalous Hall behavior when magnetic. We successfully doped the rare-earth element Tb into Bi1.08Sb0.9Te2S single crystals, inducing antiferromagnetic order below 10 K. Transport is dominated by surface states below 150 K due to an in-gap Fermi level, displaying strong 2D Shubnikov-de Haas oscillations at low temperatures.

March 13, 2023
Advanced Materials

Large Magnetic Gap in a Designer Ferromagnet heterostructure

We grew a sandwich heterostructure of magnetic MnBi2Te4 and topological Bi2Te3 using molecular beam epitaxy. Angle-resolved photoemission spectroscopy revealed hexagonally warped massive Dirac fermions and a large 75 meV bandgap. The gap vanishes above the Curie temperature, confirming its magnetic proximity origin, providing a promising platform to achieve the high-temperature quantum anomalous Hall effect.

March 8, 2022

Defects, band bending and ionization rings in MoS2

Chalcogen vacancies in transition metal dichalcogenides act as donor dopants and sources of disorder, but their electronic structure remains controversial. Using STM and STS on sulphur vacancies in bulk MoS2, we observed spectroscopic features dispersing in space and energy. These arise from tip-induced band bending causing bias-dependent vacancy ionization, showing that defect spectra do not simply reflect in-gap density of states.

February 24, 2022
ACS Applied materials & Interfaces

Formation of a Stable Surface Oxide in MnBi2Te4 Thin Films

We studied the atmospheric stability of MnBi2Te4 thin films using synchrotron photoemission, transport, and AFM. After two days, a 2 nm oxide layer passivates the surface, confining oxidation to the top two layers while preserving the bulk. Samples maintain metallic conduction and show minimal doping, offering new avenues for processing and passivating future magnetic topological devices.

January 20, 2022