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Experimental signatures for quantum anomalies in the Weyl semimetal NbP

Johannes Gooth (IBM, Rüschlikon)

Weyl semimetals are materials where electrons behave effectively as a kind of massless relativistic particles known as Weyl 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 an enhancement of thermoelectrical transport in a magnetic field, even in flat spacetime, opening the door to experimentally probe such type of anomalies in Weyl semimetals. I will present experimental signatures of the chiral and the mixed axial-gravitational anomaly in the magneto-thermoelectric transport of NbP.