# Quantum theory of the Intrinsic Orbital Magnetoelectric Effect in itinerant electron systems at finite temperatures

## TL;DR

This paper investigates the intrinsic orbital magnetoelectric effect in itinerant electron systems at finite temperatures, revealing its origin from the Fermi sea and its enhancement near Dirac points in $ ext{PT}$-symmetric metals.

## Contribution

It introduces a finite-temperature theory for the intrinsic orbital ME response in metals using the Kubo formula, emphasizing the role of the Fermi sea and $ ext{PT}$-symmetry.

## Key findings

- Intrinsic orbital ME effect originates from the Fermi sea and is dissipation-independent.
- In $ ext{PT}$-symmetric systems, extrinsic effects vanish, making the intrinsic effect dominant.
- The intrinsic ME effect is enhanced near Dirac points in a $ ext{PT}$-symmetric model.

## Abstract

Magnetization can be induced by an electric field in systems without inversion symmetry $\mathcal{P}$ and time-reversal symmetry $\mathcal{T}$. This phenomenon is called the magnetoelectric (ME) effect. The spin ME effect has been actively studied in multiferroics. The orbital ME effect also exists and has been mainly discussed in topological insulators at zero temperature. In this paper, we study the intrinsic orbital ME response in metals at finite temperature using the Kubo formula. The intrinsic response originates from the Fermi sea and does not depend on the dissipation. Especially in systems with $\mathcal{PT}$-symmetry, the extrinsic orbital ME effect becomes zero, and the intrinsic ME effect is dominant. We apply the response tensor obtained in this work to a $\mathcal{PT}$-symmetric model Hamiltonian with antiferromagnetic loop current order demonstrating that the intrinsic ME effect is enhanced around the Dirac points.