Superconductivity provides access to the chiral magnetic effect of an unpaired Weyl cone
Abstract: Massless spin-1/2 particles, so called Weyl fermions, remain unobserved as elementary particles, but they have now been realized as quasiparticles in a variety of crystals known as Weyl semimetals. Weyl fermions appear in pairs of left-handed and right-handed chirality, occupying a pair of cones in the Brillouin zone. The pairing is enforced by the chiral anomaly: A magnetic field induces a current of electrons in a Weyl cone, flowing along the field lines in the chiral zeroth Landau level. The current in the Weyl cone of one chirality has to be canceled by a current in the Weyl cone of opposite chirality, to ensure zero net current in equilibrium. The generation of an electrical current density j along an applied magnetic field B, the so called chiral magnetic effect has been observed as a dynamic, nonequilibrium phenomenon --- but it cannot be realised in equilibrium because of the fermion doubling. After an elementary introduction to chiral anomaly, I will show how superconductivity offers a way to avoid this cancellation, by means of a flux bias that gaps out a Weyl cone jointly with its particle-hole conjugate. The remaining gapless Weyl cone and its particle-hole conjugate represent a single fermionic species, with renormalized charge e* and a single chirality +/- set by the sign of the flux bias. As a consequence, the chiral magnetic effect is no longer cancelled in equilibrium but appears as a supercurrent response j=(e*e/h^2)μ B along the magnetic field at chemical potential μ.
Reminder: Tea and cookies will be in the seminar room before the seminar.