Optical conductivity in multiferroic GaV${}_4$S${}_8$ and GeV${}_4$S${}_8$: Phonons and electronic transitions

Abstract

We report on optical spectroscopy on the lacunar spinels GaV${}_4$S${}_8$ and GeV${}_4$S${}_8$ in the spectral range from 100 to 23000 cm${}^{-1}$ and for temperatures from 5 to 300 K. These multiferroic spinel systems reveal Jahn-Teller driven ferroelectricity and complex magnetic order at low temperatures. We study the infrared-active phonon modes and the low-lying electronic excitations in the cubic high-temperature phase, as well as in the orbitally and in the magnetically ordered low-temperature phases. We compare the phonon modes in these two compounds, which undergo different symmetry-lowering Jahn-Teller transitions into ferroelectric and orbitally ordered phases, and exhibit different magnetic ground states. We follow the splitting of the phonon modes at the structural phase transition and detect additional splittings at the onset of antiferromagnetic order in GeV${}_4$S${}_8$. We observe electronic transitions within the $d$-derived bands of the V${}_4$ clusters and document a significant influence of the structural and magnetic phase transitions on the narrow electronic band gaps.

12 pages, 10 figures

References in corpus (8)

• Multiferroicity and skyrmions carrying electric polarization in GaV4S8
• Spin-phonon coupling in antiferromagnetic chromium spinels
• Polar Dynamics at the Jahn-Teller Transition in Ferroelectric GaV4S8
• On the multiferroic skyrmion-host GaV4S8
• Unusual Ferroelectricity Induced by the Jahn-Teller Effect: A Case Study on Lacunar Spinel Compounds
• Structural, magnetic, electric, dielectric, and thermodynamic properties of multiferroic GeV4S8
• Terahertz Dielectric Analysis and Spin-Phonon Coupling in Multiferroic GeV${}_4$S${}_8$
• Tuning orbital-selective correlation effects in superconducting Rb${}_{0.75}$Fe${}_{1.6}$Se${}_{2-z}$S${}_z$

Cited by in corpus (10)

• Assessing exchange-correlation functional performance in the chalcogenide lacunar spinels GaM${}_4$Q${}_8$ (M = Mo, V, Nb, Ta; Q = S, Se)
• Macroscopic Manifestation of Domain-wall Magnetism and Magnetoelectric Effect in a Néel-type Skyrmion Host
• Magnetic avalanche of non-oxide conductive domain walls
• Infrared nanoscopy down to liquid helium temperatures
• Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure
• Structural, magnetic and insulator-to-metal transitions under pressure in the GaV4S8 Mott insulator: A rich phase diagram up to 14.7 GPa
• Excitations and relaxation dynamics in multiferroic GeV4S8 studied by THz and dielectric spectroscopy
• Establishing magneto-structural relationships in the solid solutions of the skyrmion hosting family of materials: GaV${}_4$S${}_{8-y}$Se${}_y$
• Charge density functional plus $U$ calculation of lacunar spinel GaM${}_4$Se${}_8$ (M = Nb, Mo, Ta, and W)
• Optical, dielectric, and magnetoelectric properties of ferroelectric and antiferroelectric lacunar spinels