Physics Colloquium: Prof. Ki-Seok Kim

A Weyl metal is a new state of matter that has been recently discovered  in tantalum arsenide (TaAs),  a crystal with strong spin-orbit interaction and inversion symmetry-breaking and in Bi1−xSbx (x ∼ 3%) in a  magnetic fields.

Landauʼs Fermi-liquid theory is the standard model for metals, characterized by the existence of electron quasiparticles near a Fermi surface as long as Landauʼs interaction parameters lie below critical values for instabilities. Recently this fundamental paradigm has been challenged by the physics of strong spin–orbit coupling, although the concept of electron quasiparticles remains valid near the Fermi surface, where Landauʼs Fermi-liquid theory fails to describe the electromagnetic properties of this novel metallic state, referred to as Weyl metal. A novel ingredient is that such a Fermi surface encloses a Weyl point with definite chirality, referred to as a chiral Fermi surface, which can arise from breaking of either time reversal or inversion symmetry in systems with strong spin–orbit coupling, responsible for both the Berry curvature and the chiral anomaly. As a result, electromagnetic properties of the Weyl metallic state are described not by conventional Maxwell equations but by axion electrodynamics, where Maxwell equations are modified with a topological-in-origin spatially modulated θ (r)E · B term.

This novel metallic state was realized recently in Bi1−xSbx around x ∼ 3% under magnetic fields, where the Dirac spectrum appears around the critical point between the normal semiconducting (x < 3%) and topological semiconducting phases (x > 3%) and the time reversal symmetry breaking perturbation causes the Dirac point to split into a pair of Weyl points along the direction of the applied magnetic field for a very strong spin–orbit coupled system.

In this review we discuss how the topological structure of both the Berry curvature and the chiral anomaly (axion electrodynamics) gives rise to anomalous transport phenomena in − Bi1 xSbx around x ∼ 3% under magnetic fields, thus modifying the Drude model of Landauʼs Fermi liquids.

The colloquium will be held by:

Prof. Ki-Seok Kim, Postech, Pohang  (Link to homepage)

Where: Lecture Hall in Research III

When:   17:15 h

Host: Prof. Dr. Stefan Kettemann, Professor of Physics | Dept. of Physics & Earth Sciences

Email: s.kettemann@jacobs-university.de, Tel: +49 421 200-3521,
Link to Homepage: http://skettemann.user.jacobs-university.de