Effective electromagnetic Lagrangians in the derivative expansion method

Abstract We calculate the effective electromagnetic Lagrangian up to the lowest-order corrections in the derivatives for two fermionic systems of interest in condensed matter physics in the linearized approximation of the tight-binding Hamiltonian near the Fermi level in the Brillouin zone: (i) the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> description of the simplest Weyl semimetal and (ii) the massive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> electrodynamics, which can serve as a model for the interface between two <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> topological insulators. We employ the derivative expansion method which directly provides local effective Lagrangians and allows selecting from the outset both the powers of the electromagnetic potential to be considered together with the number of relevant derivatives. We find new higher-order derivative corrections to Carroll-Field-Jackiw electrodynamics. In general, the new terms we find either have a similar structure or constitute a relativistic generalization of some recent phenomenological proposals found in the literature. In this way, they should be incorporated into these proposals for assessing the relative significance of all the terms included up to a given order.