Electronic and phonon excitations in α-RuCl${}_3$

Abstract

We report on THz, infrared reflectivity and transmission experiments for wave numbers from 10 to 8000 cm${}^{-1}$ ($\sim$ 1 meV - 1 eV) and for temperatures from 5 to 295 K on the Kitaev candidate material α-RuCl${}_3$. As reported earlier, the compound under investigation passes through a first-order structural phase transition, from a monoclinic high-temperature to a rhombohedral low-temperature phase. The phase transition shows an extreme and unusual hysteretic behavior, which extends from 60 to 166 K. In passing this phase transition, in the complete frequency range investigated we found a significant reflectance change, which amounts almost a factor of two. We provide a broadband spectrum of dielectric constant, dielectric loss and optical conductivity from the THz to the mid infrared regime and study in detail the phonon response and the low-lying electronic density of states. We provide evidence for the onset of an optical energy gap, which is of order 200 meV, in good agreement with the gap derived from measurements of the DC electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue shift on increasing temperatures.

arXiv comment18 pages, 7 figures

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Cited by in corpus (23)

• Models and Materials for Generalized Kitaev Magnetism
• Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in $\alpha$-RuCl${}_3$
• Heisenberg-Kitaev physics in magnetic fields
• Thermodynamic evidence of fractionalized excitations in α-RuCl3
• Cavity-induced quantum spin liquids
• Field evolution of magnons in $\alpha$-RuCl${}_3$ by high-resolution polarized terahertz spectroscopy
• Field induced magnon excitation and in gap absorption of Kitaev candidate RuCl3
• Magnon dispersion and dynamic spin response in three-dimensional spin models for $\alpha$-RuCl${}_3$
• Polarization-resolved Raman spectroscopy of α-RuCl3 and evidence of room temperature two-dimensional magnetic scattering
• Resonant inelastic x-ray scattering study of $\alpha$-RuCl${}_3$: a progress report
• Magnetic field-dependent low-energy magnon dynamics in $\alpha$-RuCl3
• Kitaev Quantum Spin Liquids
• THz excitations in α-RuCl3: Majorana fermions, rigid-plane shear and compression modes
• Susceptibility anisotropy and its disorder evolution in models for Kitaev materials
• Multiple Spin-Orbit Excitons and the Electronic Structure of $\alpha$-RuCl${}_3$
• Evidence for magnetic fractional excitations in a Kitaev quantum-spin-liquid candidate $\alpha$-RuCl${}_3$
• Sub-gap optical response across the structural phase transition in van der Waals layered α-RuCl${}_3$
• Acoustic phonon dispersion of $\alpha$-RuCl${}_3$
• Electronic structure of $\mathbf{\alpha }$-RuCl${}_3$ by fixed-node and fixed-phase diffusion Monte Carlo methods
• Non-local features of the spin-orbit exciton in Kitaev materials
• Giant anisotropic magnetoresistance in few-layer α-RuCl3 tunnel junctions
• First-principles study of bulk stacking, $J_{\mathrm{eff}}$ picture, magnetic Hamiltonian, $g$ factors, and structural distortions of $\alpha$-RuCl${}_3$
• The Role of the Third Dimension in Searching Majorana Fermions in $\alpha$-RuCl${}_3$ via Phonons