Speaker
Description
The nonequilibrium generation of orbital magnetization by applied electric fields is a central problem in the emerging field of orbitronics [1,2]. Its theoretical description, however, is challenging because the conventional expression for orbital magnetization involves the position operator, which is ill-defined under periodic boundary conditions. Although the modern theory of orbital magnetization overcomes this difficulty by reformulating the problem in terms of Bloch states [3], its extension to nonequilibrium systems and beyond the clean-crystal limit [4,5] remains incomplete.
Here, we present a general real-space formalism for nonequilibrium orbital magnetization that avoids explicit use of the position operator and is directly applicable to systems lacking perfect translational symmetry, including disordered and quasiperiodic materials. The orbital magnetization response is extracted from the current-current response function at first order in the wave vector of the applied electric field and is formulated entirely in terms of traces of operators in a basis-independent manner. The resulting expressions are manifestly gauge invariant and position-independent. The trace-based formulation is ideally suited to large-scale numerical calculations using the Kernel Polynomial Method, enabling simulations of system sizes that are inaccessible to conventional approaches and providing an efficient framework for investigating disorder effects. We demonstrate the versatility of the formalism through numerical tight-binding calculations of the magnetoelectric effect in a disordered two-dimensional CuO2 loop current model for different types of disorder.
References:
[1]A. Johansson, J. Phys.: Condens. Matter 36 423002 (2024)
[2] T. Cysne et al., npj Spintronics 3, 39 (2025)
[3]Davide Ceresoli et al., Phys. Rev. B 74, 024408 (2006)
[4]O. Ocaña et al., SciPost Phys. 14, 118 (2023)
[5]K. Shinada et al., Phys. Rev. B 107, 094106 (2023)
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