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Superconductors (materials that conduct electricity without resistance) have fascinated physicists for more than a century. While conventional superconductors are well understood, a new class of materials known as topological superconductors has attracted intense interest in recent years.

These superconductors have been reported to be capable of hosting Majorana quasiparticles, exotic states that could change the field of fault-tolerant quantum computing. Yet many of the fundamental properties of these novel bulk topological superconductors remain relatively unknown, leaving open questions about how their unusual electronic states interact with the underlying crystal lattice.

In a new study conducted by Professor Guo-qing Zheng, along with Kazuaki Matano, S. Takayanagi, K. Ito of Okayama University and Professor H. Nakao of High Energy Accelerator Research Organization (KEK), published in on August 22, 2025, the researchers report that the doped topological insulator Cu_xBi₂Se₃ undergoes tiny but spontaneous distortions in its crystal lattice as it enters the superconducting state.

This marks the first clear evidence of a topological superconductor that is capable of coupling to the crystal lattice and distorting it during the superconducting transition, a phenomenon unknown to physicists until now.

Superconductivity is typically associated with electron pairing that leaves the host lattice untouched. But in Cu_xBi₂Se₃, a rare spin-triplet topological superconductor, Prof. Zheng and colleagues observed distortions of approximately 100 parts per million when the superconducting order parameter, known as the d vector, tilted away from the crystal's high-symmetry axes. No such distortion was found in more symmetric states or in highly doped crystals where a chiral superconducting state dominates.

"Our work demonstrates that lattice distortion is not just a byproduct but a key diagnostic for identifying unconventional superconducting phases," added Prof. Zheng. The study builds on earlier nuclear magnetic resonance experiments that showed broken spin-rotation symmetry in Cu_xBi₂Se₃, a signature of spin-triplet pairing. The researchers established a direct link between the superconducting symmetry and the material's structural response by combining synchrotron X-ray diffraction with angle-resolved susceptibility measurements.

Beyond its fundamental significance, the discovery has practical implications. "A topological superconductor can be applied to fault-tolerant quantum computing. It is important to know the basic properties of the material when fabricating quantum bits from such superconductors," Prof. Zheng said.

Bulk topological superconductors remain scarce, and their properties are poorly understood. This has limited their use outside the laboratory. The researchers believe the new results could help change that: "Bulk topological superconductors have not been used in industry simply because the materials are rare and their properties are poorly known. Our work will advance industrial applications in making next-generation quantum computers."

The findings also resonate with broader studies of multicomponent superconductors, including iron-based materials, Kagome lattices, and twisted bilayer graphene. All of these systems may host exotic states where the superconducting order parameter couples to lattice degrees of freedom.

Still, the researchers caution that open questions remain. The strength of the coupling appears sensitive to defects introduced during crystal growth, suggesting that sample preparation and purity will play a central role in future experiments and potential applications.

This research provides condensed matter physicists with a new lens to probe topological quantum states by uncovering how superconductivity can distort a lattice, bringing the field one step closer to harnessing these exotic properties for quantum technologies.