A New Path to Superconductivity
In a superconductor, pairs of electrons are coaxed together at low temperature into a collective state that flows without resistance. Lattice vibrations provide the nudging in conventional superconductors; in the high-Tc cuprates, antiferromagnetic fluctuations do the job. Now Xiao-Gang Wen of MIT and his collaborators have identified conditions under which superconductivity can arise from the electrons’ own mutual electrostatic repulsion [1]. Their theory predicts multiple superconducting states, some of which have exotic properties.
In previous work, Wen and his collaborators looked at the fractional quantum Hall effect and explored the possibility that a superconducting state could be formed by the effect’s quasiparticles—anyons, whose collective behavior is intermediate between fermions and bosons. Recent experimental discoveries inspired the MIT theorists to apply their approach to electrons, which, being fully fermionic, are a special case of anyons. As with the anyon superconductivity, the new theory requires a two-dimensional host. Another defining characteristic is that electrons’ energy must increase as the fourth power of their momentum k rather than having the usual k2 dependence.
The MIT team predicted many different superconducting states, all of which have chirality—meaning the electrons flow with a symmetry-breaking handedness. Another exotic property of some of the states is that the charge condensations are quartets of electrons rather than pairs. As is the case for regular superconductivity, for these states to appear, their energies must be lower than that of their parent state—the state from which they emerge upon cooling. That parent state is one of two exotic electronic states characterized by strong repulsive interactions, but the team’s calculations are currently not reliable enough to identify which. However, the requisite k4 dispersion has already been observed in twisted bilayers.
–Charles Day
Charles Day is a Senior Editor for Physics Magazine.
References
- M. Kim et al., “Topological chiral superconductivity beyond pairing in a Fermi liquid,” Phys. Rev. B 111, 014508 (2025).