Magnetic topological insulators

Realisation of QAHE

Intrinsic magnetic topological insulator featuring spontaneous time-reversal symmetry breaking enabling robust quantum anomalous hall effect.

image of maintenance crew working on aircraft
MnBi2Te4 breaks time-reversal symmetry intrinsically. In thin films, the hybridizsation of top and bottom surface states creates a topological mass gap. When the Fermi level lies within this gap, the system exhibits the quantised Hall effect without an external magnetic field, enabling dissipationless transport.

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

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

3. XRD

A non-destructive technique used to analyse the atomic structure and phase of the epitaxially grown heterostructures.

4. PPMS and MPMS

Versatile sample measurement systems for characterising the electronic and magnetic properties of heterostructures with varying temperatures and external magnetic fields.

What we've discovered

Read our papers here
Recent
Older (>2 yrs)
No items found.
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
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
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