Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa$_4$

TL;DR

This study identifies EuGa4 as a magnetic Weyl nodal ring semimetal with tunable topological states, exhibiting extremely large, non-saturating magnetoresistance and distinct Landau quantization, promising for electronic and spintronic applications.

Contribution

The paper reports the discovery of EuGa4 as a new magnetic Weyl nodal ring semimetal with unique Landau quantization and giant magnetoresistance, expanding the class of tunable magnetic topological semimetals.

Findings

EuGa4 hosts Weyl nodal ring states near the Fermi level.

EuGa4 exhibits magnetoresistance exceeding 200,000% at 2 K and 14 T.

Magnetoresistance remains unsaturated up to 40 T.

Abstract

Magnetic topological semimetals (TSMs) allow for an effective control of the topological electronic states by tuning the spin configuration, and therefore are promising materials for next-generation electronic and spintronic applications. Of magnetic TSMs, Weyl nodal-line (NL) semimetals likely have the most tunability, and yet they are the least experimentally studied so far due to the scarcity of material candidates. Here, using a combination of angle-resolved photoemission spectroscopy and quantum oscillation measurements, together with density functional theory calculations, we identify the square-net compound EuGa4 as a new magnetic Weyl nodal ring (NR) semimetal, in which the line nodes form closed rings in the vicinity of the Fermi level. Remarkably, the Weyl NR states show distinct Landau quantization with clear spin splitting upon application of a magnetic field. At 2 K in a field of 14 T, the transverse magnetoresistance of EuGa4 exceeds 200,000%, which is more than two orders of magnitude larger than that of other known magnetic TSMs. High field magnetoresistance measurements indicate no saturation up to 40 T. Our theoretical model indicates that the nonsaturating MR naturally arises as a consequence of the Weyl NR state. Our work thus point to the realization of Weyl NR states in square-net magnetic materials, and opens new avenues for the design of magnetic TSMs with very large magnetoresistance.