2017/03/29 by Johannes Gooth, Anna Corinna Niemann, Tobias Meng +14 · 298 citations
Materials Science · Physics and Astronomy · #Anomaly (physics) #Chiral anomaly #Conformal anomaly #Conformal field theory #Fermion #Gauge anomaly #Gauge theory #Geometry #Graphene research and applications #Gravitation #Gravitational anomaly #Gravitational field #Introduction to gauge theory #Massless particle #Mixed anomaly #Physics #Quantum and electron transport phenomena #Quantum mechanics #Semimetal #Spacetime #Topological Materials and Phenomena #Weyl semimetal #cond-mat.mes-hall #cond-mat.mtrl-sci #hep-th
paper · pdf · doi:10.1038/nature23005
published in Nature 547(7663), 324-327 (Nature Portfolio)
arxiv created 2017/03/29 · openalex publication_date 2017/07/01 · arxiv updated 2017/09/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Weyl semimetals are materials where electrons behave effectively as a kind of massless relativistic particles known asWeyl fermions. These particles occur in two flavours, or chiralities, and are subject to quantum anomalies, the breaking of a conservation law by quantum fluctuations. For instance, the number of Weyl fermions of each chirality is not independently conserved in parallel electric and magnetic field, a phenomenon known as the chiral anomaly. In addition, an underlying curved spacetime provides a distinct contribution to a chiral imbalance, an effect known as the mixed axial-gravitational anomaly, which remains experimentally elusive. However, the presence of a mixed gauge-gravitational anomaly has recently been tied to thermoelectrical transport in a magnetic field, even in flat spacetime, opening the door to experimentally probe such type of anomalies in Weyl semimetals. Using a temperature gradient, we experimentally observe a positive longitudinal magnetothermoelectric conductance (PMTC) in the Weyl semimetal NbP for collinear temperature gradients and magnetic fields (DT || B) that vanishes in the ultra quantum limit. This observation is consistent with the presence of a mixed axial-gravitational anomaly. Our work provides clear experimental evidence for the existence of a mixed axial-gravitational anomaly of Weyl fermions, an outstanding theoretical concept that has so far eluded experimental detection.