All That Matters

One of the fundamental concepts of quantum mechanics is that objects can be described as waves, whether they are electrons, atoms, light, anything really, even your cat (or that of Erwin Schrödinger). And of course, if the equations that describe their wavefunctions are identical, objects will behave in the same way. Even if they are fundamentally different physical entities.

Two papers published this week highlight just how far this analogy can go. In one study a gas of ultracold atoms behaves like electrons in a crystal, whereas in the other study the ultracold atoms show quantum effects known from laser physics. Atoms behaving like electrons as well as light.

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Go to any condensed-matter physics meeting, and topological insulators are prominent on the agenda, and talks on the topic attract large audiences. For good reason. Topological insulators promise nothing less than a revolution in electronics. Even though as their name suggests topological insulators are electrically insulating, they are conducting on their surface. And unlike regular conductors, these surface currents flow without the electrons being thrown off the track by most (albeit not all) scattering effects from impurities. This is one of their key features that ultimately may lead to smaller and faster electronic devices.

Even though first experimental breakthroughs have been achieved since 2006 in two-dimensional (thin films) of HgTe with similar properties, the tell-tale surface currents haven’t been observed in three-dimensional topological insulators such as the widely studied Bi₂Se₃ and Bi₂Te₃. So far, samples have not reached a sufficient purity and researchers had to make do with indirect characterisation experiments rather than direct measurements of electrical transport. This has now changed. In a study published in today’s issue of Science, Robert Cava, Nai Phuan Ong and colleagues from Princeton University report on the first experiments demonstrating electron conduction on the surface of Bi₂Te₃.

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Fridge magnets, and related magnets used in homes and offices, are made from the ceramic BaFe₁₂O₁₉, whose annual commercial production reaches 830,000 tons a year. Contrary to what their mundane use suggests, the physics of these magnets is rather unusual. They belong to a rare class of materials whose magnetism can be controlled with electric voltages and vice versa, which offers a new way of controlling magnetic fields in applications such as information storage (other than putting notes up on your fridge!).

Unfortunately, in most of these ceramics such effects are confined to low temperatures and have been mainly of interest to physicists only. Tsuyoshi Kimura and colleagues from Osaka University may now have changed this. They have discovered that in a close relative of fridge magnets, Sr₃Co₂Fe₂₄O₄₁, coupled interactions between magnetic and electric properties occur even at room temperature. “This demonstrates that such magnets can be used for other practical usages,” says Kimura. Their work is published online this week in Nature Materials.

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