Thermal chiral anomaly in the magnetic-field induced ideal Weyl phase of Bi1-xSbx topological insulators

The chiral anomaly is the predicted break down of chiral symmetry in a Weyl semimetal with monopoles of opposite chirality when an electric field parallel to a magnetic field is applied. It occurs because of charge pumping from a positive chirality to a negative chirality monopole. Experimental observation of this fundamental effect has been plagued by concerns about the pathways of the current. Here, we unambiguously demonstrate the thermal analog of the chiral anomaly in topological insulator bismuth-antimony alloys driven into an ideal Weyl semimetal state by a Zeeman field, with the chemical potential pinned at the Weyl points, and in which the Fermi surface has no trivial pockets. The experimental signature is a large enhancement of the thermal conductivity in an applied magnetic field parallel to the thermal gradient that follows the Wiedemann-Franz law above 60 K. Absence of current flow avoids extrinsic effects that plague electrical measurements.