Strange topological materials are popping up everywhere physicists look

‘Fragile topology’ is the latest addition to a group of quantum phenomena that give materials exotic — and exciting — properties.

The mathematics hidden in materials keeps getting more exotic. Topological states of matter — which derive exotic properties from their electrons’ ‘knotty’ quantum states — have shot from rare curiosity to one of the hottest fields in physics. Now, theorists are finding that topology is ubiquitous — and recognizing it as one of the most significant ways in which solid matter can behave.

In the past few years, physicists have identified a ‘fragile’ version of topology that might occur in almost all crystalline solids, according to a preprint posted in May1. Another study, published2 last month in Nature, describes hints of a fragile state in the electrons of a carbon-based device — which, if confirmed, would be the first experimental evidence for fragile topology.

It is too early to say whether these discoveries will have a major impact on practical materials. But researchers have found that they might help to explain certain kinds of superconductivity, and say that the phenomenon is also likely to be important in photonics, technologies that carry information in light pulses rather than electrons. Fragile topology could also have implications for researchers who use supercomputers to simulate the behaviour of materials.

The latest studies show that fragile topology “is not just a radical, academic rabbit hole that people are going down”, says Ashvin Vishwanath, a theoretical physicist specializing in condensed matter at Harvard University in Cambridge, Massachusetts. “I am having a hard time keeping up with the field, even though it’s just a year old.”

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