On thermal Nieh-Yan anomaly in topological Weyl materials
J. Nissinen+ 1), G. E. Volovik+*
+Low Temperature Laboratory, Department of Applied Physics, Aalto University, P. O. Box 15100, FI-00076 AALTO, Finland
*Landau Institute for Theoretical Physics Russian Academy of Sciences, 119334 Moscow, Russia
Abstract
We discuss the possibility of gravitational Nieh-Yan anomaly of the
type
in
topological Weyl materials, where
T is temperature and is the effective or emergent
torsion. As distinct from the non-universal parameter Λ in the
conventional (zero temperature) Nieh-Yan anomaly - with canonical
dimensions of momentum - the parameter γ is dimensionless. This
suggests that the dimensionless parameter is fundamental, being
determined by the geometry, topology and number of the number of chiral
quantum fields without any explicit non-universal UV scales. This
conforms with previous results in the literature, as well as spectral
flow calculations using torsional magnetic field at finite temperature.