Anomalous Nernst effect in strained graphene coupled to a substrate inducing a time-reversal symmetry breaking

Abstract

A novel anomalous Nernst effect in graphene engineered by a strain and coupled to an environment with a broken time-reversal breaking is predicted. We consider the Haldane model (1988 Phys. Rev. Lett. 61 2015) including a uniaxial strain and analyze explicitly the time-reversal symmetry behavior. We find in this case that the total Nernst coefficient contributed by the two Dirac cones is no longer zero. For further insight we study the interplay of the stagger-field-induced gap of the substrate and the time-reversal symmetry-breaking-induced gap. The former preserves the opposite signs of the Berry curvatures, whereas in the latter the Berry curvatures possess the same sign. For a weak time reversal breaking (TRB), the total Nernst signal experiences a sign change as the Fermi level increases. When TRB is large, the total Nernst coefficient exhibits a two-peak structure varying with the Fermi level. Another feature is that the anomalous Nernst signal has an anti-symmetric profile with respect to the neutral Dirac point instead of the symmetric behavior known for the case of an external magnetic field. We further find a robust six-leaf modulation of the total Nernst coefficient as the direction of the strain is varied.