Transport theory and spin-transfer physics for frustrated magnets

TL;DR

This paper develops a transport theory for electrons in frustrated magnetic conductors, incorporating spin-exchange interactions and hydrodynamic equations, revealing potential new Hall effects in these complex systems.

Contribution

It introduces a novel transport framework based on the doped Hubbard model and slave-boson formalism for frustrated magnets, including spin-transfer torque and Yang-Mills field effects.

Findings

New contributions to charge and spin currents depending on order parameter variations

Microscopic derivation for the triangular lattice Heisenberg antiferromagnet

Potential for unanticipated Hall physics in frustrated magnetic systems

Abstract

We study the electron dynamics in magnetic conductors with frustrated interactions dominated by isotropic exchange. We present a transport theory for itinerant carriers built upon the (single-band) doped Hubbard model and the slave-boson formalism, which incorporates the spin-exchange with the magnetically frustrated background into the representation of electron operators in a clear and controllable way. We also formulate hydrodynamic equations for the itinerant charge and spin degrees of freedom, whose currents contain new contributions that depend on the spatiotemporal variations of the order parameter of the frustrated magnet, which are described by Yang-Mills fields. Furthermore, we elucidate the transfer of angular momentum from the itinerant charge fluid to the magnet (i.e., the spin-transfer torque) via reciprocity arguments. A detailed microscopic derivation of our effective theory is also provided for one of the simplest models of frustrated magnetism, namely the Heisenberg antiferromagnet on a triangular lattice. Our findings point towards the possibility of previously unanticipated Hall physics in these frustrated platforms.