Magnetic fluctuations and spin-spirals in single-layer FeSe

TL;DR

This study uses first-principles calculations to explore magnetic fluctuations and spin-spirals in monolayer FeSe, revealing flat spin-wave energies and explaining experimental electronic band features through magnetic state averaging.

Contribution

It provides new insights into the magnetic fluctuation landscape of monolayer FeSe and links these fluctuations to observed electronic structures, considering substrate effects.

Findings

The (pi,pi) CL-AFM mode is lowest in energy.

Spin-wave energy E(q) is very flat around the CB-AFM configuration.

Substrate and oxygen vacancies enhance CB-AFM-like fluctuations.

Abstract

The magnetic properties of monolayer FeSe films are investigated via first-principles spin-spiral calculations. Although the (pi,pi) collinear antiferromagnetic (CL-AFM) mode is lowest in energy, the spin-wave energy E(q) - which exhibits intrinsic non-Heisenberg behavior - is found to be extremely very flat over a large region of the two-dimensional Brillouin zone centered at the checkerboard antiferromagnetic (CB-AFM) q=0 configuration, giving rise to a sharp peak in the spin density of states. Considering the paramagnetic state as an incoherent average over spin-spiral states, we find that resulting electronic band states around the Fermi level closely resemble the bands of the CB-AFM configuration - not the CL-AFM one - and thus providing a natural explanation of the angle-resolved photoemission observations. The presence of the SrTiO3(001) substrate, both with and without interfacial oxygen vacancies, is found to reduce the energy difference between the CB-AFM and CL-AFM states and hence enhancing the CB-AFM-like fluctuations.