SCIENTISTS FIND FIRST TYPE I SUPERCONDUCTOR TO BREAK TIME-REVERSAL SYMMETRY

Researchers led by Anshu Kataria at the Indian Institute of Science Education and Research (IISER) Bhopal have identified the first type I superconductor known to break time-reversal symmetry, according to a study published in the journal Physical Review Letters. The material, a compound called YbSb₂, displayed the property when cooled to extremely low temperatures, the researchers said. Time-reversal symmetry is the principle that a physical system behaves the same way whether time runs forward or backward. Every previously known superconductor that breaks this symmetry was a type II material, the team said.

Superconductors conduct electricity with no resistance when cooled to ultra-low temperatures, and are classed as type I or type II according to how they respond to magnetic fields. The researchers grew single crystals of YbSb₂, whose atomic structure appears in both conventional and unconventional superconductors, and confirmed it was a type I material by testing its magnetic behaviour. They then cooled the crystals to near absolute zero and implanted muons, particles sensitive to faint magnetic fields, directly into the material. As YbSb₂ entered its superconducting state, the researchers detected spontaneous internal magnetic fields, evidence they said would not exist if time-reversal symmetry had been preserved.

The study authors said the fields likely arise from an unconventional superconducting state known as the internally antisymmetric nonunitary triplet state. Unconventional and type II superconductors have generally been regarded as more exotic than type I materials because they require specialised engineering, according to the researchers. The team said the discovery shows type I superconductors can display quantum behaviour previously seen only in more complex materials. Researchers said the findings could eventually inform the design of quantum computing technologies.