Superconducting proximity effect to the block antiferromagnetism in K$_{y}$Fe$_{2-x}$Se$_{2}$

TL;DR

This paper investigates how superconductivity influences block antiferromagnetism in K$_{y}$Fe$_{2-x}$Se$_{2}$, proposing a proximity effect explanation for magnetic moment suppression observed experimentally.

Contribution

It introduces a two-orbital model to analyze the superconducting proximity effect on block AFM layers, highlighting the significance of interlayer coupling and weak electron correlations.

Findings

Proximity effect can significantly suppress magnetic moments.

Suppression is more pronounced with d-wave superconductivity.

Results align semi-quantitatively with neutron experiments.

Abstract

Recent discovery of superconducting (SC) ternary iron selenides has block antiferromagentic (AFM) long range order. Many experiments show possible mesoscopic phase separation of the superconductivity and antiferromagnetism, while the neutron experiment reveals a sizable suppression of magnetic moment due to the superconductivity indicating a possible phase coexistence. Here we propose that the observed suppression of the magnetic moment may be explained due to the proximity effect within a phase separation scenario. We use a two-orbital model to study the proximity effect on a layer of block AFM state induced by neighboring SC layers via an interlayer tunneling mechanism. We argue that the proximity effect in ternary Fe-selenides should be large because of the large interlayer coupling and weak electron correlation. The result of our mean field theory is compared with the neutron experiments semi-quantitatively. The suppression of the magnetic moment due to the SC proximity effect is found to be more pronounced in the d-wave superconductivity and may be enhanced by the frustrated structure of the block AFM state.