Abstract
Weyl semimetals exhibit unusual surface states and anomalous transport phenomena. It is hard to manipulate the band structure topology of specific Weyl materials. Topological transport phenomena usually appear at very low temperatures, which sets challenges for applications. In this work, we demonstrate the band topology modification via a weak magnetic field in a ferromagnetic Weyl semimetal candidate, Co2MnAl, at room temperature. We observe a tunable, giant anomalous Hall effect (AHE) induced by the transition involving Weyl points and nodal rings. The AHE conductivity is as large as that of a 3D quantum AHE, with the Hall angle (ΘH) reaching a record value (tan {Theta }^{H}=0.21) at the room temperature among magnetic conductors. Furthermore, we propose a material recipe to generate large AHE by gaping nodal rings without requiring Weyl points. Our work reveals an intrinsically magnetic platform to explore the interplay between magnetic dynamics and topological physics for developing spintronic devices.
Highlights
Weyl semimetals exhibit unusual surface states and anomalous transport phenomena
Our recent success in growing Co2MnAl single crystals with the L21 phase has enabled us to observe its fascinating properties originating from the band topology. We found that this material exhibits very large anomalous Hall conductivity (AHC), up to 1300 Ω−1 cm−1 at room temperature; more noticeably, its room temperature anomalous Hall angle (AHA) ΘH reaches a new record value among all magnetic conductors, with tan ΘH 1⁄4 0:21
From our electron diffraction analyses, we have observed the (111) diffraction spot in the electron diffraction pattern taken along the [110] zone axis (Fig. 1d), indicating that our Co2MnAl crystals surely have the L21 structure phase. This is further corroborated by scanning transmission electron microscopy (STEM) imaging shown in Fig. 1c, where the periodic, alternating distribution of Mn and Al can be seen clearly from the atomic intensity line due to Z-contrast
Summary
Weyl semimetals exhibit unusual surface states and anomalous transport phenomena. It is hard to manipulate the band structure topology of specific Weyl materials. The Weyl semimetal (WSM)[1,2,3,4,5,6,7] is characterized by the linear band-crossing points, called Weyl points, which exhibits monopole-type structure of the Berry curvature[8,9], leading to many exotic properties, such as the Fermi arc surface states[1], the chiral anomaly effect[10,11], and the anomalous Hall effect (AHE)[12,13] This topological phase has been discovered in materials such as TaAs14–18 and MoTe219–22 recently. These materials provide ideal platforms to tune the band structure topology
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