Collective excitations in proximity-coupled spin singlet-triplet frequency even-odd superconducting condensates: Multicomponent superconductivity in MgB2/half-metallic manganite nanostructures

Artificial nano-heterostructures have attracted special interest as new functional materials nowadays. We briefly review the experimental results obtained on proximitized nanocomposites based on half-metallic manganites and two-band s-wave superconductor MgB2. The experimental data and theoretical models give the physical background that proximity-induced long-range superconducting state in these hybrid heterostructures can be qualitatively and quantitatively understood within the framework of unconventional multicomponent superconducting condensates: proximity-coupled spin singlet-triplet frequency even-odd superconducting charge carriers. The key physics behind these quantum effects is the fluctuation superconductivity of half-metallic manganites. Collective excitations (Higgs and Leggett modes) associated with the gap’s magnitude and relative phase oscillations of singlet/triplet-spin and even/odd-frequency superconducting order parameters experimentally detected in MgB2/half-metallic manganite hybrid structures are among the base arguments of this conclusion. The results evidence that the superconductor–half-metallic manganite heterostructures are promising functional quantum materials with unconventional spin-triplet superconducting pairing.