Artículo
H-ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons
Massa, Nestor Emilio
; Del Campo, Leire; Holldack, Karsten; Canizarès, Aurélien; Ta Phuoc, Vinh; Kayser, Paula; Alonso, José Antonio
Fecha de publicación:
10/2020
Editorial:
American Physical Society
Revista:
Physical Review B
ISSN:
2469-9950
e-ISSN:
2469-9969
Idioma:
Inglés
Tipo de recurso:
Artículo publicado
Clasificación temática:
Resumen
We report the temperature-dependent THz to mid-infrared response of hexagonal-ErMnO3 using absorption, reflectivity, and emissivity techniques from 2 to 1700 K. At low temperatures, lowest frequency vibrational modes, which extend up the lock-in ferroelectric temperature, coexist with paramagnon excitations and are associated with well-defined crystal-field rare-earth pure magnetic replicas in an intriguing phonon-magnetic convergence enhancing the multiferroic character of h-ErMnO3. Increasing the temperature, a number of vibrational bands close to the space group predicted undergo profile broadening and softening. In particular, a distinctive set of bands in the 288-329-cm-1 (300 K) range has a component whose profile is carrier screened becoming nearly fully blurred in the intermediate phase between ∼830 and ∼1500 K. Below TC∼830 K this asymmetric band, having one component still partially screened, further splits as spin phonon interaction and the tripling of the unit cell take place revealing at TN∼79 K a delicate balance of long- and short-range interactions. Ambient Raman scattering brings up evidence of a Fröhlich resonance due to Coulomb interactions between carriers and the macroscopic field linked to the corresponding longitudinal optical-phonon mode. We found it is dynamically correlated to the hexagonal c-axis negative thermal expansion. Quantitative analyses of the mid-infrared (MIR) optical conductivity show that it also plays a role in small polarons and mediates in high-temperature bipolarones. Bipolaron profiles at high temperatures change as the sample opacity increases when at ∼900 K straight stripes turn curly toward complex vortex-antivortex domain patterns in the paraelectric phase. At still higher temperatures a low-frequency Drude contribution is triggered by electron hopping signaling an insulator-metal phase transition at ∼1600 K while the MIR response suggests coexistence between single small polarons and bipolarons. On closing, we draw a parallel with improper ferroelectrics sustaining a lattice incommensurate intermediate phase and unit-cell tripling. We argue that in the h-RMnO3 (R=rare earth, Y) family of compounds the intermediate phase be considered incommensurate with onset at TINC∼1500 K and ferroelectric lock-in at TC∼830 K delimiting this regime in h-ErMnO3.
Palabras clave:
H-ErMnO3
,
ABSORBANCE, REFLECTIVITY, EMISSIVITY
,
TERAHERTZterahertz
,
POLARONS
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Articulos(CEQUINOR)
Articulos de CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Articulos de CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Citación
Massa, Nestor Emilio; Del Campo, Leire; Holldack, Karsten; Canizarès, Aurélien; Ta Phuoc, Vinh; et al.; H-ErMnO3 absorbance, reflectivity, and emissivity in the terahertz to mid-infrared from 2 to 1700 K: Carrier screening, Fröhlich resonance, small polarons, and bipolarons; American Physical Society; Physical Review B; 102; 13; 10-2020; 134305-134321
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