Researchers have identified three distinct superconducting phases in K₂Cr₃As₃, revealing a tunable platform for topological superconductivity and potential Majorana excitations.
Spin-triplet superconductors are among the rare and intriguing quantum materials today. Unlike conventional superconductors, they allow electron pairs to retain an internal spin degree of freedom, giving rise to different superconducting states. Some topological spin-triplet superconducting phases can host Majorana excitations, which may have applications in fault-tolerant quantum computing. However, identifying and controlling genuine spin-triplet superconductivity has remained challenging. Previously studied candidates often have low transition temperatures or competing states that make their intrinsic behavior difficult to understand.
A research team led by Professor Guo-qing Zheng from Okayama University investigated K₂Cr₃As₃, examining how paired electron spins and energy gaps change with temperature and magnetic field using ⁽⁵As nuclear magnetic resonance techniques. The measurements revealed three distinct superconducting phases. At low magnetic fields, the material enters Phase A, a helical state. Upon cooling, it transforms into Phase B, a chiral state where the d(k)-vector rotates 90 degrees. Both phases have point nodes in their gaps. At higher magnetic fields, Phase C emerges with a line-nodal superconducting gap structure.
According to Professor Zheng: “These results show that K₂Cr₃As₃ is not simply one type of spin-triplet superconductor. Instead, temperature and magnetic field allow us to move between distinct superconducting phases with different spin structures and topological properties.”
Phase B breaks time-reversal symmetry and its vortex cores may host Majorana excitations. Phase A is also topological and could host Majorana states at boundaries in thin films. This establishes K₂Cr₃As₃ as a platform for exploring topological quantum states relevant to future quantum computing technologies.
Journal: Physical Review Letters
DOI: 10.1103/kykd-2nj4
Article Title: Multiple Phases in K₂Cr₃As₃: A Playground for Manipulating Topological Superconductivity
Publication Date: August 21, 2026
Source: Okayama University