Tunable chirality of noncentrosymmetric magnetic Weyl semimetals in rare-earth carbides

Rajyavardhan Ray,Banasree Sadhukhan,Jorge I. Facio,Manuel Richter,Jeroen van den Brink

doi:10.1038/s41535-022-00423-z

Rajyavardhan Ray, Banasree Sadhukhan + Show 3 more

Open Access

https://doi.org/10.1038/s41535-022-00423-z

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Abstract

Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiting this experimentally is severely hampered by Weyl lattice fermions coming in pairs with opposite chirality, typically causing the net chirality picked up by experimental probes to vanish. Here, we show this issue can be circumvented in a controlled manner when both time-reversal- and inversion symmetry are broken. To this end, we investigate chirality disbalance in the carbide family RMC2 (R a rare-earth and M a transition metal), showing several members to be Weyl semimetals. Using the noncentrosymmetric ferromagnet NdRhC2 as an illustrating example, we show that an odd number of Weyl nodes can be stabilized at its Fermi surface by properly tilting its magnetization. The chiral configuration endows a topological phase transition as the Weyl node transitions across the Fermi sheets, which triggers interesting chiral electromagnetic responses. Further, the tilt direction determines the sign of the resulting net chirality, opening up a simple route to control its sign and strength.

Highlights

Since their experimental discovery in the TaAs family, Weyl semimetals continue to gain interest
We show by consideration of available experimental information and own density-functional calculations (DFT) that RMC2 compounds can be categorized in four classes: (I) Θ-symmetric and I -broken semimetals (YCoC2 and LuCoC2); (II) Θbroken and I -symmetric metals (GdRuC2); (III) both Θ- and I -broken semimetals (PrRhC2, NdRhC2, GdCoC2 and GdNiC2); and (IV) insulators (LaRhC2), the latter being of secondary interest for this work
As a proof of principle, we show for NdRhC2 and GdCoC2 how in ferromagnetic (FM) noncentrosymmetric phases tilting of the magnetization (m) along a low-symmetry direction produces a disbalance in the number of opposite chirality Weyl fermions near the Fermi surface: of all Weyl nodes the degeneracy is lifted

Summary

Introduction

Since their experimental discovery in the TaAs family, Weyl semimetals continue to gain interest. The non-trivial topology of this electronic phase follows from the geometrical properties[1] associated with electronic bands. Weyl nodes must come in pairs of opposite chirality[3]. The essential condition to enable the existence of Weyl nodes in the first place is broken spin degeneracy of Bloch states at a generic crystal momentum. This requires time-reversal symmetry (Θ) or inversion symmetry (I ) to be broken. In EuCd2As229 and EuCd2Sb230, on the other hand, a Weyl semi-metallic phase is realized for the fully spin-polarized state induced by an external magnetic field

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