Experimental signatures of the mixed axial-gravitational anomaly in the Weyl semimetal NbP

Understand

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.