Experimental Signatures of Topological Transport in Polycrystalline FeSi Thin Films

TL;DR

This study demonstrates that polycrystalline eSi thin films exhibit intrinsic topological transport phenomena, including the anomalous Hall effect and Weyl semimetal characteristics, despite disorder and polycrystallinity.

Contribution

It provides experimental evidence of topological features in disordered polycrystalline eSi films, revealing their potential as high-temperature Weyl semimetals.

Findings

Intrinsic anomalous Hall conductivity observed below 200 K.

Topological features confirmed by chiral anomaly in magnetoresistance.

Estimated Weyl point separation of approximately 0.36.

Abstract

Disorder in any form is considered to be highly detrimental to the experimental exploration of novel phenomena in quantum materials with non-trivial band topology. Contrary to established belief, clear topological features are reliably detected in the electron transport of polycrystalline 65-nm-thick \epsilon -FeSi films grown via solid-state reaction of Fe deposited on a Si(100) substrate. The observation of temperature-independent anomalous Hall conductivity \sigma_{xy}^{AHE} \sim const (\sigma_{xx)) (\sigma_{xy}^{AHE} \approx 14 uS/sq.) below 200 K firmly proves the anomalous Hall effect in this compound to be intrinsic and originating from a non-trivial Berry phase. The discovered scaling dominates over the nanoscale (\sim 40 nm) polycrystalline texture and is robust to temperature crossover between bulk and surface modes of electron transport. The non-trivial topological state of \epsilon-FeSi is also confirmed by a chiral anomaly both in anisotropic longitudinal magnetoresistance and planar Hall effect specific for Weyl semimetals. Relating scaled anomalous Hall conductance to a "quantized" Hall response of a Weyl semimetal the distance between two Weyl points has been estimated as (k_{+}^{W}-k_{-}^{W})/(2\pi) \approx 0.36. Our findings confirm the topological origin of electron transport in the polycrystalline \epsilon -FeSi thin films and discover its potential as a new high temperature and noble metal-free Weyl semimetal.