Antiferromagnetic Order in Epitaxial FeSe Films on SrTiO3

Abstract

Single monolayer FeSe film grown on a Nb-doped SrTiO_{3}(001) substrate shows the highest superconducting transition temperature (T_{C}∼100 K) among the iron-based superconductors (iron pnictides), while the T_{C} value of bulk FeSe is only ∼8 K. Although bulk FeSe does not show antiferromagnetic order, calculations suggest that the parent FeSe/SrTiO_{3} films are antiferromagnetic. Experimentally, because of a lack of a direct probe, the magnetic state of FeSe/SrTiO_{3} films remains mysterious. Here, we report direct evidence of antiferromagnetic order in the parent FeSe/SrTiO_{3} films by the magnetic exchange bias effect measurements. The magnetic blocking temperature is ∼140 K for a single monolayer film. The antiferromagnetic order disappears after electron doping.

Strong enhancement of magnetic order from bulk to stretched monolayer FeSe as Hund’s metals

“…The suppressed low-energy excitation and tendency for a magnetic order rather result from the local two-particle vertex, which includes effects of overall increase of local orbital occupations away from the integer filling by doping, which should suppress the fluctuating moment and enhance charge fluctuations. Zero ordered moment is obtained in the stripe-type AFM calculation for 0.12 e − /Fe doped ML FeSe, in consistence with our χ 00 m result in the PM phase and also with the suppressed magnetic order by electron doping found experimentally 35 as mentioned above. This large sensitivity of magnetic order on doping therefore results from local correlations, which are well described within the DFT + DMFT method.…”

“…The stabilization of the AFM phase in ML FeSe on SrTiO 3 has been also predicted by previous DFT calculations 29,33,34 , however, with large ordered moments of over 2 μ B , which are likely overestimated as is a well-known general property of DFT on IBS. A recent experimental work indeed confirmed an AFM order in this system using magnetic exchange bias effect measurement 35 , though neither the ordering vector nor the ordered moment could be determined. It is also found that the magnetic order disappears for the electron doped sample where superconductivity can arise.…”

The Computational 2D Materials Database: high-throughput modeling and discovery of atomically thin crystals

“…This prediction is consistent with the recent experimental observation that monolayer FeSe deposited on SrTiO 3 exhibits AFM order. 48…”

Edge States at Nematic Domain Walls in FeSe Films

“…However, the checkerboard AFM might develop in the FeSe domain boundaries, since the electronic properties, such as the broken two-fold symmetry and the in-plane lattice expansion, are similar to that in 1 UC FeSe /STO, 6 in which a recent study shows experimental evidence for AFM order. 29 DFT calculations are carried out to study the possible topological origin of the edge states with AFM. For a two-dimensional (2D) film, the topological invariance usually oscillates with the number of layers 30,31 .…”