Researchers at IFW Dresden and the Cluster of Excellence ct.qmat announced on November 19 that they had identified a new form of superconductivity in the crystalline material PtBi₂. This form displayed a topological behavior and an electron-pairing pattern that had never been seen before.
The findings of this experiment promise a route to generating stable Majorana particles, regarded as the building blocks of future quantum technologies. The new material platform is also key for tackling fault-tolerant quantum computing.
PtBi₂ is intrinsic, with no complex engineering or exotic conditions necessary. This condition opens pathways to control Majoranas, engineer custom qubit architectures, and build more stable quantum devices.
The new six-fold symmetry
Most superconductors allow electron pairing in all directions, forming a smooth, symmetrical superconducting state. Even in high-temperature cuprate superconductors, the pairing exhibits a four-fold symmetry.
But, PtBi₂ is the first of its kind to show a six-fold restricted pairing, a feature tied to the crystal’s underlying three-fold symmetry.
“We have never seen this before. Not only is PtBi₂ a topological superconductor, but the electron pairing that drives this superconductivity is different from all other superconductors we know of,” said Dr. Sergey Borisenko, a researcher on the experiment.
“We don’t yet understand how this pairing comes about,” he continued.
Automatic formation of Majorana particles
The researchers confirmed that the superconducting state in PtBi₂ naturally produces Majorana particles. These particles are elusive, long-hypothesized quasiparticles that behave like “split electrons” and are immune to many forms of quantum noise.
Theoretical work led by Prof. Jerone van den Brink shows that these Majorana modes are confined to the material’s edges. Intriguingly, by cutting the crystal or by engineering step edges, researchers can generate as many edge-bound Majoranas as needed.
Dissecting PtBi₂’s unusual behavior
To help explain the finding, the researchers break PtBi₂’s unusual behavior into four steps. First, topological surface states force electrons to live only on the crystal’s outer layers; the states remain intact even if the material is cut.
In the second step, these surface electrons become superconducting at low temperatures. The interior stays metallic during this period, forming a natural “superconductor sandwich.”
Third, the pairing on these surfaces shows an unprecedented six-fold symmetry, with electrons in six key directions refusing to pair at all.
Finally, this topological superconductivity automatically produces Majorana particles along the edges — particles that can be shifted or controlled using magnetic fields, thinning the material, or creating artificial step edges.
Majorana pairs can encode information in a way that is inherently protected from errors; hence, they are considered a leading candidate for stable qubits in topological quantum computers.
The discovery of a naturally occurring material that hosts such particles without requiring complex layering, artificial interfaces, or magnetic fields represents a major leap forward..
What lies ahead
The researchers now aim to explore how to manipulate the Majorana states, for instance, by thinning the crystal to tune its interior from metallic to insulating or by applying magnetic fields to shift the location of the quasiparticles.
With PtBi₂’s unprecedented superconducting symmetry and robust topological edges, scientists may now have a practical platform for building the next generation of quantum devices.
The research was published in the journal Nature.