The condensate of electron quadruplets is a proposed state of matter in which Cooper pairs are formed but do not exhibit long-range order, but electron quadruplets do.
Such states emerge in systems with multiple broken symmetries due to the partial melting of the underlying low-temperature order, which destroys the condensates of Cooper pairs but preserves the condensates formed by pairs of preformed fermion pairs.
[3] Another example is "quartic metal" phase [4][5] is related to but distinct from those superconductors explained by the standard BCS theory; rather than expelling magnetic field lines as in the Meissner effect, it generates them, a spontaneous Nernst effect that indicates the breaking of time-reversal symmetry.
[7] In systems with a greater number of broken symmetries, theoretical studies have demonstrated the existence of charge-6e and more complex orders.
[8][9] After the theoretical possibility was raised, observations consistent with electron quadrupling were published using hole-doped Ba1-xKxFe2As2 in 2021,[6][10] with evidence of vestigial quadrupling reported in CsV3Sb5 soon after, in early 2022.