The Role of the Third Dimension in Searching Majorana Fermions in $\alpha$-RuCl${}_3$ via Phonons

Abstract

Understanding phonons in $\alpha$-RuCl${}_3$ is critical to analyze the controversy around the observation of the half-integer thermal quantum Hall effect. While many studies have focused on the magnetic excitations in $\alpha$-RuCl${}_3$, its vibrational excitation spectrum has remained relatively unexplored. We investigate the phonon structure of $\alpha$-RuCl${}_3$ via inelastic neutron scattering experiments and density functional theory calculations. Our results show excellent agreement between experiment and first principles calculations. After validating our theoretical model, we extrapolate the low energy phonon properties. We find that the phonons in $\alpha$-RuCl${}_3$ that either propagate or vibrate in the out-of-plane direction have significantly reduced velocities, and therefore have the potential to dominate the observability of the elusive half integer plateaus in the thermal Hall conductance. In addition, we use low-energy interlayer phonons to resolve the low temperature stacking structure of our large crystal of $\alpha$-RuCl${}_3$, which we find to be consistent with that of the $R\bar{3}$ space group, in agreement with neutron diffraction.

The first two authors contributed equally

References in corpus (13)

• Non-Abelian Anyons and Topological Quantum Computation
• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Scattering Continuum and Possible Fractionalized Excitations in $\alpha$-RuCl${}_3$
• Long range magnetic ordering in Na${}_2$IrO${}_3$
• Successive magnetic phase transitions in $\mathbf{\alpha }$-RuCl${}_3$: XY-like frustrated magnet on the honeycomb lattice
• Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in $\alpha$-RuCl${}_3$
• Sample dependence of the half-integer quantized thermal Hall effect in the Kitaev candidate $\alpha$-RuCl${}_3$
• Field-induced intermediate ordered phase and anisotropic interlayer interactions in $\alpha$-RuCl${}_3$
• Scale-invariant magnetic anisotropy in RuCl${}_3$ at high magnetic fields
• Electronic and phonon excitations in α-RuCl${}_3$
• Phonon renormalization in the Kitaev quantum spin liquid
• Rare-earth chalcohalides: A family of van der Waals layered Kitaev spin liquid candidates
• Temperature evolution of the phonon dynamics in the Kitaev spin liquid