Phys : Seminars / 25.05.2017 - İnanç Adagideli : Superconductivity provides access to the chiral magnetic effect of an unpaired Weyl cone

Superconductivity provides access to the chiral magnetic effect of an unpaired Weyl cone

İnanç Adagideli
Department of Physics, Sabancı University, Istanbul
25 May 2017, Thursday, 14:40
Cavid Erginsoy Seminar Room, Physics Department, 3rd floor

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.

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