Recent experimental results have revealed signatures of unconventional electron condensates that go beyond the standard Cooper pair paradigm.
In multicomponent and unconventional superconductors, the proliferation of topological phase excitations can indeed destroy the phase coherence among Cooper pairs while preserving coherence among pairs of Cooper pairs. The resulting beyond-mean-field phases are characterized by a four-electron order parameter and accompanied by spontaneous symmetry breaking.
In this talk, I will discuss recent theoretical and experimental advances on electron quadruplet condensates in multiband superconductors and twisted bilayer graphene, and present new results on possible electron quadruplets emerging from a nematic superconducting ground state.