Rare i-wave State in PtBi2 Open New Path for Majorana Qubits
Quantum Leap: PtBi2 Has Ultra-Rare “i-wave” Superconductivity
PtBi2 exhibits a novel superconductivity discovered by an international collaboration. Using cutting-edge spectroscopic approaches, the researchers identified i-wave pairing symmetry, a rare electronic state that could revolutionise topological quantum computing.
Solving the Symmetry Issue
Superconductivity is usually defined by electron pairing and flow. In “textbook” materials like niobium and lead, electrons create s-wave pairs with zero angular momentum. More uncommon materials with d-wave symmetry, such the high-temperature cuprate superconductors discovered decades ago, contain “nodes” where superconductivity practically disappears in the gap.
Beyond these recognised states, PtBi2 discovery is significant. In the Weyl semimetal PtBi2, they identified i-wave pairing, which corresponds to l=6 angular momentum. Never before has unconventional superconductivity above the d-wave level (l=2) been detected spectroscopically. The material's intricate symmetry comes from its trigonal crystal structure and point group symmetry, A2.
Atomic precision
Discovery was made utilising angle-resolved photoemission spectroscopy (ARPES) to map electron energy and momentum. Using a low-energy laser source (6 eV), the scientists achieved “unprecedented clarity” by focussing on Fermi arcs, which are surface-only electronic states.
Their results show that the PtBi2 surface becomes superconducting below 10 K, whereas the rest of the material remains metallic. The researchers found Fermi arc-centered gap nodes in this superconducting surface. These nodes are more than physical oddities—they define the substance's unusualness.
The Majorana Link
These nodes greatly impact topological matter. Because PtBi2's Fermi-arc states are non-degenerate and chiral, the superconducting order parameter changes along the arc, creating surface Majorana cones.
Majorana fermions interact with their own antiparticles. Researchers believe these cones create powerful, zero-energy Majorana flat bands near surface step or hinge borders. This makes PtBi2 surfaces uncommon, topological i-wave superconductors and a viable material platform for generating and manipulating Majorana bound states.
A “anomalous” topological superconductor appears on PtBi2. More than four Majorana cones are needed in a typical 2D system. However, PtBi2 features six Majorana cones on top and six on bottom, a 3D system-only layout.
Challenges and Quantum Computing Path
Despite the excitement, PtBi2 is not ready for quantum computers yet, experts said. One challenge is the coexistence of gapless Majorana states with a metallic bulk, which may interfere with the sensitive quantum information in Majorana modes.
Ultrathin samples to remove bulk modes or a magnetic field to disturb time-reversal symmetry are among the group's suggestions. If this symmetry is disrupted, Majorana cones may “gap out” and leave zero-dimensional bound states or chiral Majorana edge modes suitable for topological quantum computation's “braiding” operations.
New Material Science Chapter
Since i-wave superconductivity was discovered, PtBi2 is now a special material. While there exists potential for intrinsic topological superconductivity in materials like Sr2RuO4 or heavy-fermion systems, experimental results have been inconsistent. This study's ARPES data clarity provides perhaps the strongest evidence for an intrinsic topological superconductor.
As scientists evaluate these discoveries, they will likely focus on determining the mechanism behind this rare i-wave combination. Cuprates require strong electron interactions, but PtBi2's extremely delocalised electronic states suggest a different, unexplained source for its unique properties.
You can understand these superconducting states by comparing electron pairing to a staged dance. A typical s-wave superconductor's dancers appear to move in a perfect circle from every angle. D-wave superconductors dance more intricately, like a flower with four petals, stopping at four nodes. In the recently discovered i-wave state of PtBi2, the dance is an intricate, high-frequency geometry with twelve petals, forming a complex motion-stillness pattern that produces the mysterious Majorana particles at its border.