Amazing stuff!
"... Until recently, every superconductor known to do this was a type II material. But in a study published in the journal Physical Review Letters, researchers report the discovery of a type I superconductor that breaks time-reversal symmetry too. ..."
From the abstract:
"The spontaneous breaking of time-reversal symmetry is a hallmark of unconventional superconductivity, typically observed in type-II superconductors. Here, we report evidence of time-reversal symmetry breaking in the type-I superconductor YbSb2. Zero-field muon spin relaxation and rotation (𝜇SR) measurements reveal spontaneous internal magnetic fields emerging just below the superconducting transition, while transverse-field 𝜇SR confirms a fully gapped type-I superconducting state.
Our first-principles calculations identify YbSb2 as a ℤ2 topological metal hosting a Dirac nodal line near the Fermi level.
Symmetry analysis within the Ginzburg-Landau framework indicates an internally antisymmetric nonunitary triplet (INT) state as the most probable superconducting ground state. Calculations based on an effective low-energy model further suggest that this INT state may host gapless Majorana surface modes, pointing to the possibility of topological superconductivity in YbSb2.
Our results highlight YbSb2 as a unique material platform where type-I superconductivity coexists with triplet pairing and nontrivial topology."
Observation of Time-Reversal Symmetry Breaking in the Type-I Superconductor YbSb2 (no public access)
Observation of Time-Reversal Symmetry Breaking in the Type-I Superconductor YbSb (preprint, open access)
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