Gapless Dirac magnons in CrCl3

John A. Schneeloch; Yu Tao; Yongqiang Cheng; Luke Daemen; Guangyong Xu; Qiang Zhang; Despina Louca

doi:10.1038/s41535-022-00473-3

Gapless Dirac magnons in CrCl₃

John A. Schneeloch, Yu Tao, Yongqiang Cheng, Luke Daemen, Guangyong Xu, Qiang Zhang, Despina Louca

Research output: Contribution to journal › Article › peer-review

12 Scopus citations

Abstract

Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX₃ (X = Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr₃ and CrI₃, gapless Dirac magnons are present in bulk CrCl₃, with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac K point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above T_N. Moreover, on cooling below ~50 K, an anomalous increase in the a-axis lattice constant and a hardening of a ~26 meV phonon feature are observed, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above T_N.

Original language	English
Article number	66
Journal	npj Quantum Materials
Volume	7
Issue number	1
DOIs	https://doi.org/10.1038/s41535-022-00473-3
State	Published - Dec 2022

Funding

This work has been supported by the Department of Energy, Grant number DE-FG02-01ER45927. A portion of this research used resources at the High Flux Isotope Reactor and the Spallation Neutron Source, which are DOE Office of Science User Facilities operated by Oak Ridge National Laboratory. Computing resources for DFT simulations were made available through the VirtuES and the ICE-MAN projects, funded by Laboratory Directed Research and Development program and Compute and Data Environment for Science (CADES) at ORNL. This work has been partly supported by the National Institute of Standards and Technology, US Department of Commerce, in providing neutron research facilities used in this work. Certain commercial materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. This work has been supported by the Department of Energy, Grant number DE-FG02-01ER45927. A portion of this research used resources at the High Flux Isotope Reactor and the Spallation Neutron Source, which are DOE Office of Science User Facilities operated by Oak Ridge National Laboratory. Computing resources for DFT simulations were made available through the VirtuES and the ICE-MAN projects, funded by Laboratory Directed Research and Development program and Compute and Data Environment for Science (CADES) at ORNL. This work has been partly supported by the National Institute of Standards and Technology, US Department of Commerce, in providing neutron research facilities used in this work. Certain commercial materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

Funders	Funder number
Compute and Data Environment for Science
U.S. Department of Energy	DE-FG02-01ER45927
National Institute of Standards and Technology
U.S. Department of Commerce
Oak Ridge National Laboratory
Laboratory Directed Research and Development

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10.1038/s41535-022-00473-3

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title = "Gapless Dirac magnons in CrCl3",

abstract = "Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX3 (X = Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr3 and CrI3, gapless Dirac magnons are present in bulk CrCl3, with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac K point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above TN. Moreover, on cooling below ~50 K, an anomalous increase in the a-axis lattice constant and a hardening of a ~26 meV phonon feature are observed, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above TN.",

author = "Schneeloch, {John A.} and Yu Tao and Yongqiang Cheng and Luke Daemen and Guangyong Xu and Qiang Zhang and Despina Louca",

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AU - Schneeloch, John A.

AU - Tao, Yu

AU - Cheng, Yongqiang

AU - Daemen, Luke

AU - Xu, Guangyong

AU - Zhang, Qiang

AU - Louca, Despina

PY - 2022/12

Y1 - 2022/12

N2 - Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX3 (X = Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr3 and CrI3, gapless Dirac magnons are present in bulk CrCl3, with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac K point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above TN. Moreover, on cooling below ~50 K, an anomalous increase in the a-axis lattice constant and a hardening of a ~26 meV phonon feature are observed, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above TN.

AB - Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX3 (X = Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr3 and CrI3, gapless Dirac magnons are present in bulk CrCl3, with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac K point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above TN. Moreover, on cooling below ~50 K, an anomalous increase in the a-axis lattice constant and a hardening of a ~26 meV phonon feature are observed, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above TN.

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Gapless Dirac magnons in CrCl₃

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