Far- and mid-infrared emission and reflectivity of orthorhombic and cubic 
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: Polarons and bipolarons

Massa, N. E.; Campo, Leire del; Holldack, K.; Phuoc, V. Ta; Echegut, Patrick; Kayser, Paula

doi:10.1103/physrevb.98.184302

Cited by 2 publications

(1 citation statement)

References 61 publications

(62 reference statements)

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“…In this scenario one of the dimerized electron pair constituting the bipolaron hopes to a next near neighbor small polaron site changing the mid-infrared profile within picture that turns indistinguishable from what we already reported for the high temperature metal-insulator transition in orthorhombic O-ErMnO3 at about the same temperatures. 89 I.e., as shown in Fig. 9 the reproduction of the optical conductivity at ~1624 K is a plain superposition of contributions product of the bipolaron dissociation as for small polarons coexisting with Drude thermal activated itinerant carriers.…”

Section: E Small Polaron and Higher Temperature Bipolaronsmentioning

confidence: 83%

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

et al. 2020

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We report the temperature dependent THz to mid-infrared response of hexagonal-ErMnO3 using absorption, reflectivity, and emissivity techniques from 2 K 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 K 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 takes 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 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.

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Section: E Small Polaron and Higher Temperature Bipolaronsmentioning

confidence: 83%

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

et al. 2020

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Small-polaron-induced infrared opacification in rutile TiO2

Arrieta

González-Fernández

Echániz

et al. 2021

Journal of Applied Physics

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The infrared emittance of single-crystal rutile TiO2 has been measured from room temperature to 2000 K in dry air for two polarization states. A very strong thermally induced opacification phenomenon has been found, with the sample being completely opaque in the near-infrared range several hundred K before its melting point. A large contribution from small-polaron hopping conduction can explain this anomalous degree of opacification, much stronger than similar phenomena present in other octahedrally coordinated oxide materials. These quasiparticles manifest in the high-temperature optical conductivity as a thermally activated contribution, with an activation energy close to that of DC conductivity. The small-polaron nature of this phenomenon is strengthened by the observation of broad near-infrared bands.

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Far- and mid-infrared emission and reflectivity of orthorhombic and cubic ErMnO3 : Polarons and bipolarons

Cited by 2 publications

References 61 publications

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

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

Small-polaron-induced infrared opacification in rutile TiO2

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