Recently, physicists have discovered a new type of superconductor called “platinum bismuth” that hides an electron world unseen by people before. The surface of this material exhibits superconductivity, allowing electrons to pass through with zero resistance, while the interior remains in a normal metallic state. What’s even more intriguing for physicists is that the pairing pattern of surface electrons in “platinum bismuth” breaks all known superconductivity physical rules and holds the potential to advance the field of quantum science.
Collaborating with scientists from various countries, the Leibniz Institute for Solid State and Materials Research in Germany (IFW Dresden) has found unexpected properties in this shiny gray crystal “platinum bismuth” (PtBi₂) superconductor, which could potentially serve as a new platform for quantum computers and quantum technologies, driving advancements in the field of quantum science. This research has been published in the scientific journal “Nature.”
While scientists discovered the superconducting properties of the surface of “platinum bismuth” in 2024, the latest in-depth research has revealed that the pairing of its surface electrons is vastly different from the current known superconductors. Traditional cuprate high-temperature superconductors often exhibit “d-wave” symmetry (quadrupole symmetry), whereas “platinum bismuth” is the first superconductor confirmed to have an “i-wave” symmetry (hexapole symmetry).
The research team points out that the abnormality of “platinum bismuth” stems from its unique topological properties (meaning that the material maintains its geometric properties under continuous spatial deformations). This restricts certain electrons to be strictly bound to the upper and lower surfaces of the crystal. The topological protection in “platinum bismuth” is very stable, and the electron state is difficult to disrupt unless the crystal structure is altered or a strong magnetic field is applied.
One of the unique aspects of “platinum bismuth” is that regardless of the crystal’s size, the surface-bound electrons always match those inside. If the crystal is cut in half, the newly exposed surface immediately forms the same bound electrons.
Furthermore, at low temperatures, surface electrons in “platinum bismuth” begin to pair up and move without resistance. However, the internal electrons of this material do not participate in pairing and behave like normal electrons. Researchers describe this structure as a “natural superconducting sandwich” structure, where the outer surface exhibits excellent conductivity while the interior behaves like a regular metal.
What astonishes researchers even more is the presence of elusive natural “Majorana particles” at the edges of these superconducting surfaces. These particles are considered ideal materials for building future fault-tolerant quantum bits (qubits).
The “Majorana particles” mainly appear in pairs and collectively behave like a single electron. When separated, they can be used to resist environmental noise, which is crucial for “topological quantum computing.” Topological quantum computing aims to create qubits with stronger resilience to noise and errors.
Due to the abnormal superconducting properties of “platinum bismuth” and the edge-bound Majorana particles that have been discovered, researchers are focusing on controlling these effects as crucial steps in utilizing “platinum bismuth” as a platform for future quantum technologies.
One strategy involves varying the material thickness to create ultra-thin samples, transitioning the material from a conductive metal to an insulator, reducing interference from internal normal electrons on the Majorana particles. Another approach is to apply a magnetic field to allow the Majorana particles to move from the crystal edges to the corners.
The research team mentions that only a few materials are currently believed to demonstrate topological superconductivity (TSC), but these materials lack strong experimental evidence except for “platinum bismuth,” which is the actual topological superconductor. Therefore, this study also confirms that “platinum bismuth” provides a new practical pathway for producing Majorana particles, which have long been pursued in the field of condensed matter physics.
Dr. Sergey Borisenko, a paper author from the Leibniz Institute for Solid State and Materials Research in Dresden, Germany, expressed to the institute’s press office, ” ‘Platinum bismuth’ is a topological superconductor with surface superconductivity electron pairing mechanisms different from those we previously knew. However, we still do not understand how this pairing is generated.”
Jeroen van den Brink, the director of the Theory of Solid State Physics at IFW, added, “Theoretical calculations indicate that the topological superconductivity of ‘platinum bismuth’ automatically generates Majorana particles, bound to the edges of the material. In fact, we can artificially create step edges in the crystal to obtain any desired Majorana particles.”