Abstract
We report measurements of optical absorption in the zigzag antiferromagnet α-RuCl3 as a function of temperature T, magnetic field B, and photon energy ω 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.
| Original language | English |
|---|---|
| Article number | 227201 |
| Journal | Physical Review Letters |
| Volume | 119 |
| Issue number | 22 |
| DOIs | |
| State | Published - Nov 28 2017 |
Funding
We thank N. P. Armitage, L. Balents, C. Batista, A. Potter, M. Serbyn, S. Winter, R. Valenti, and A. Vishwanath for helpful discussions, and H. Bechtel and M. Martin for support at the Advanced Light Source beam lines 1.4.3 and 1.4.4. Terahertz spectroscopy was performed at Lawrence Berkeley National Laboratory in the Spin Physics program supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515. A. L. and L. W. were supported by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant No. GBMF4537 to J. O. at U.C. Berkeley. The work at ORNL was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC05-00OR22725. A. B. and S. E. N. were supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, Division of Scientific User Facilities. P. L.-K. and D. M. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant No. GBMF4416.