Antiferromagnetic Resonance and Terahertz Continuum in α-RuCl_{3}

A Little; Liang Wu; P Lampen-Kelley; A Banerjee; S Patankar; D Rees; C A Bridges; J-Q Yan; D Mandrus; S E Nagler; J Orenstein

doi:10.1103/PhysRevLett.119.227201

Antiferromagnetic Resonance and Terahertz Continuum in α-RuCl_{3}

Phys Rev Lett. 2017 Dec 1;119(22):227201. doi: 10.1103/PhysRevLett.119.227201. Epub 2017 Nov 28.

Authors

A Little^{1

2}, Liang Wu^{1

2

3}, P Lampen-Kelley^{4

5}, A Banerjee⁶, S Patankar^{1

2}, D Rees^{1

2}, C A Bridges⁷, J-Q Yan⁸, D Mandrus^{4

5}, S E Nagler^{6

9}, J Orenstein^{1

2}

Affiliations

¹ Department of Physics, University of California, Berkeley, California 94720, USA.
² Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
³ Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
⁴ Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA.
⁵ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
⁶ Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA.
⁷ Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA.
⁸ Material Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge,Tennessee 37830, USA.
⁹ Bredesen Center, University of Tennessee, Knoxville, Tennessee 37966, USA.

PMID: 29286790
DOI: 10.1103/PhysRevLett.119.227201

Abstract

We report measurements of optical absorption in the zigzag antiferromagnet α-RuCl_{3} as a function of temperature T, magnetic field B, and photon energy ℏω in the range ∼0.3-8.3 meV, using time-domain terahertz spectroscopy. Polarized measurements show that threefold rotational symmetry is broken in the honeycomb plane from 2 to 300 K. We find a sharp absorption peak at 2.56 meV upon cooling below the Néel temperature of 7 K at B=0 that we identify as the magnetic-dipole excitation of a zero-wave-vector magnon, or antiferromagnetic resonance (AFMR). With the application of B, the AFMR broadens and shifts to a lower frequency as long-range magnetic order is lost in a manner consistent with transitioning to a spin-disordered phase. From a direct, internally calibrated measurement of the AFMR spectral weight, we place an upper bound on the contribution to the dc susceptibility from a magnetic excitation continuum.