Sr2RuO4 and the first TRS-breaking superconductors (1998)
Zero-field muon spin relaxation suggested that Sr2RuO4, a type-II superconductor, generates spontaneous internal fields on entering its superconducting state, evidence of broken time-reversal symmetry. The interpretation has been debated since.
The finding made Sr2RuO4 the archetypal test case for TRS breaking in superconductors.
For nearly three decades, spontaneous TRS breaking was observed only in type-II materials.
YbSb2 is the first type-I superconductor to show the same signature, breaking the pattern Sr2RuO4 helped establish.
