Quantum Q&A with Melissa Henderson

Dr. Melissa Henderson is a researcher at the Institute for Quantum Computing (IQC) and the University of Waterloo’s Department of Physics and Astronomy. Her research considers the scattering of neutral particles known as neutrons, and their relation to quantum materials.

Henderson’s research, alongside her PhD supervisor Dr. Dmitry Pushin – a professor at IQC and the Department of Physics and Astronomy – was recently published in Nature Physics in the paper Three-dimensional neutron far-field tomography of a bulk skyrmion lattice. We reached out to her to learn about these latest findings.

Can you explain the topic you researched in this paper?

I study nanoscale magnetic structures known as skyrmions, which are present in some magnetic crystals. They are formed by the collective alignment of magnetic properties from individual atoms which twist into tornado-like vortexes significantly larger than atomic scales.

Magnetic skyrmions are primarily concerned with a concept known as topology. A simple way to visualize topology is to consider the deformations of a continuous object, such as a balloon. A balloon without any holes is said to have a topology of zero. We can stretch or compress it, but still maintain its spherical, continuous structure and therefore its topology. If we wished to alter the topology of the balloon, we could introduce a discontinuity, such as a hole. In doing this we provide energy to the system to pop the balloon.

Instead of holes in balloons, topology in skyrmions is a measure of how their magnetic properties, also known as electron spin, twist and wind in their orientations. This representation of topology can be visualized by imagining the electron spins in a cross-section of the skyrmion wrapping around a sphere. Typically, these spins cover the sphere once, pointing straight out from the centre, which corresponds to a topology of one. However, skyrmions can also have higher integer topologies where they wrap around this sphere multiple times.

What is something that excites you about your work?

I work at the cutting edge of both neutron and quantum materials physics, unifying the two fields to push the boundaries of what we know and what we can measure. It’s exciting to develop new?investigative/characterization?tools which could?provide unprecedented access to magnetic phenomena and uncover novel physics. I also like that we can develop our own instrumentation and new probes that push the frontiers of the fields – that’s where the new science happens.

It is also exciting that our?measurement/characterization techniques and results may transcend those of just neutron techniques and skyrmion systems,?enabling the examination of a broader set of topological phases and excitations across a diverse range of quantum materials, spanning a variety of length, scales, dimensions, and interactions.

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Can you explain your new research findings?

Prior to our work, existing skyrmion probing methods primarily utilized electrons and x-rays, both of which have limited penetration depths in the materials they are measuring. Therefore, these measurement tools require thinned and geometrically confined systems which completely change the shapes, sizes, and transition pathways of skyrmions.

Our latest finding uses so a probing technique called Small Angle Neutron Scattering to circumvent this fundamental restriction of electron and x-ray techniques as neutrons are one of the few particles that can pass through a larger crystal, known as a bulk sample. One drawback, however, is that neutrons provide a 2D average of the magnetic moments that they interacted with in the sample. To counteract this and retain the depth information, we rotated the sample and measured it from a variety of different angles, in much the same way as a CT scan uses 2D x-rays to develop a 3D image. This allowed us to visualize the 3D nature and internal structures of skyrmions in large crystal samples, known as bulk samples, for the very first time.

This result is the first demonstration of how these skyrmion tubes form and interact in bulk systems through topological defects, providing novel insight into their stabilization mechanisms and nucleation and annihilation pathways.?

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What are the real-world implications of these findings?

An emerging field known as spintronics uses electron spin instead of current to hold digital information. Our findings may reimagine current skyrmion-based spintronic frameworks, motivating new designs which exploit the 3D nature of skyrmions, which offer?new symmetries, degrees of freedom, and dynamical behaviors compared to those of thin and confined systems.?

These results open the door to a new era in the characterization of bulk quantum materials and the three-dimensional engineering of skyrmion spintronic devices. Moreover, these results offer fundamental insights into topological defect and phase behaviors, which may be applied to understand a variety of physical systems spanning superconductors to liquid crystals.?

#QuantumComputing #Spintronics #MagneticMaterials #QuantumPhysics