Intrinsic Nonlinear Gyrotropic Magnetic Effect Governed by Spin-Rotation Quantum Geometry

TL;DR

This paper develops a quantum-kinetic framework linking spin-resolved quantum geometry to nonlinear gyrotropic magnetic responses in 2D systems, revealing new geometric effects and symmetry-dependent transport phenomena.

Contribution

It introduces the spin-rotation quantum geometric tensor as a fundamental quantity governing nonlinear magnetic responses, expanding understanding beyond conventional electric-field effects.

Findings

Off-diagonal sector controlled by Zeeman symplectic and metric connections.

Diagonal sector dictated by spin-rotation quantum metric and Berry curvature.

Symmetries selectively activate conduction and displacement channels.

Abstract

Nonlinear magnetic response driven by time-periodic magnetic fields offers a distinct route to probe spin-resolved quantum geometry beyond conventional electric-field-driven nonlinear effects. While linear magnetic responses depend on the Zeeman quantum geometric tensor, the influence of generalized spin-rotation quantum geometries on nonlinear responses has not been established. Here, we develop a microscopic quantum-kinetic framework to elucidate how the Zeeman and spin-rotation quantum geometric tensors govern nonlinear gyrotropic magnetic transport in two-dimensional systems. We derive second-order gyrotropic magnetic currents and reveal a distinct geometric separation: the off-diagonal sector is controlled by the Zeeman symplectic and metric connections, whereas the diagonal sector is dictated by the spin-rotation quantum metric and Berry curvature. This identifies the spin-rotation quantum geometric tensor as a fundamental geometric quantity unique to the nonlinear regime. Applying our theory to massless Dirac fermions, hexagonally warped topological insulator surface states, tilted massive Dirac fermions, and parity-time symmetric CuMnAs, we demonstrate how specific symmetries selectively activate conduction and displacement channels. Our findings link spin-resolved quantum geometry to nonlinear magnetic transport, offering design principles for engineering tailored nonlinear magnetic responses in optoelectronic and spintronic devices.