Superconductivity, a quantum phenomenon characterized by the absence of electrical resistance and the expulsion of magnetic fields, continues to offer fertile ground for exploring fundamental physics, especially concerning the nature of broken symmetries. One of the most intriguing avenues in this field is the study of time-reversal symmetry breaking (TRSB) in both conventional and unconventional superconductors. While conventional superconductors have historically been associated with preserved symmetries, growing evidence from muon spin rotation (μSR), Kerr effect, and other sensitive techniques has revealed TRSB signatures in certain conventional systems, challenging established paradigms. The emergence of TRSB in unconventional superconductors, such as those with non-standard pairing mechanisms or complex electronic structures, has further fueled debates regarding the interplay between symmetry, order parameters, and novel quantum phases.

Recent studies have broadened the scope of TRSB research by uncovering its manifestations in an expanding variety of superconducting families, ranging from heavy fermion compounds and cuprates to iron-based and non-centrosymmetric materials. These findings have deepened our understanding of the link between TRSB and exotic pairing states, quantum criticality, and new topological phases of matter. However, open questions remain: What microscopic mechanisms drive TRSB in distinct materials? How universal are these mechanisms across different classes of superconductors? And what novel experimental and theoretical approaches can further illuminate the implications of TRSB on superconducting properties and functionalities?

This Research Topic aims to advance our knowledge by integrating theoretical and experimental perspectives to identify, characterize, and interpret time-reversal symmetry breaking in both established and emerging superconductors. By fostering dialogue between researchers working on different materials and methodologies, this topic seeks to clarify unresolved debates, inspire novel material searches, and guide the synthesis and manipulation of superconductors for future technological applications.

To gather further insights in the mechanisms and manifestations of TRSB in superconductors, we welcome articles addressing, but not limited to, the following themes:
- Experimental detection and signatures of TRSB (e.g., μSR, polar Kerr effect, neutron scattering)
- Theoretical models and predictions for TRSB in diverse superconductors
- Relationship between TRSB and superconducting order parameters
- Comparative studies across conventional and unconventional systems
- Material discovery and design targeting TRSB phases
- Connections between TRSB and other broken symmetries in quantum materials
- Implications of TRSB for superconducting device applications

Authors

Frontiers in Electronic Materials

Superconducting Materials