Optical properties of large and small polarons and bipolarons

Emin, David

doi:10.1103/physrevb.48.13691

Cited by 428 publications

(488 citation statements)

References 25 publications

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“…Our data, however, shows a slight blue shift of the M1 MIR peak upon cooling in agreement with a small polaron scenario. 60,61 Similar temperature dependence of the MIR band has been reported in semiconducting Nd 1−x TiO 3 . 62 Although our MIR data do not contradict the small polaron interpretation, we would like to exercise caution here.…”

Section: B Mid Infrared Bandsupporting

confidence: 68%

Doping and temperature-dependent optical properties of oxygen-reducedBaTiO3−δ

et al. 2010

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We report on optical properties of reduced BaTiO 3−δ at different doping levels including insulating and metallic samples. In all the samples, including metallic one, we observe structural phase transitions from the changes of the infrared active phonon modes. Metallic ground state is confirmed by the Drude-type low-frequency optical reflectance. Similar to SrTiO 3−δ we find that the mid-infrared absorption band in BaTiO 3−δ appears and grows with an increase in the oxygen vacancy concentration. Upon decrease in temperature from 300 K, the mid-infrared band shifts slightly to higher frequency and evolves into two bands: the existing band and a new and smaller band at lower frequency. The appearance of the new and smaller band seems to be correlated with the structural phase transitions.

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Section: B Mid Infrared Bandsupporting

confidence: 68%

Doping and temperature-dependent optical properties of oxygen-reducedBaTiO3−δ

et al. 2010

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“…As pointed out by Emin [26], there are two simple limits in which absorption associated with photoionization of Holstein polarons is well understood and the optical conductivity can be calculated analytically. The first one is the weak-coupling case, where the absorption coefficient falls monotonically with increasing applied frequency.…”

Section: B Optical Conductivitymentioning

confidence: 99%

Spectral properties of the 2D Holstein polaron

Fehske

Loos

Wellein

1997

Zeitschrift für Physik B Condensed Matter

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The two-dimensional Holstein model is studied by means of direct Lanczos diagonalization preserving the full dynamics and quantum nature of phonons. We present numerical exact results for the single-particle spectral function, the polaronic quasiparticle weight, and the optical conductivity. The polaron band dispersion is derived both from exact diagonalization of small lattices and analytic calculation of the polaron self-energy.

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“…In particular, reported room-temperature electron Hall mobilities range from 0.01 to 10 cm 2 /V s. [3][4][5] In addition, the precise nature of the transport has remained unresolved. Because of the strong electron-phonon coupling in TiO 2 , electrons are described in terms of polarons, 6,7 quasiparticles consisting of an electron and accompanying lattice deformation. For a sufficiently strong electron-phonon interaction, small polarons are formed.…”

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confidence: 99%

Electron transport inTiO2probed by THz time-domain spectroscopy

et al. 2004

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Electron transport in crystalline TiO 2 ͑rutile phase͒ is investigated by frequency-dependent conductivity measurements using THz time-domain spectroscopy. Transport is limited by electron-phonon coupling, resulting in a strongly temperature-dependent electron-optical phonon scattering rate, with significant anisotropy in the scattering process. The experimental findings can be described by Feynman polaron theory within the intermediate coupling regime and allow for a determination of electron mobility. DOI: 10.1103/PhysRevB.69.081101 PACS number͑s͒: 72.40.ϩw, 71.38.Ϫk, 72.10.Di, 72.20.Dp Titanium dioxide (TiO 2 ) is a wide-band-gap semiconductor with properties of both technological and fundamental interest. In addition to diverse industrial applications, TiO 2 has recently gained importance for new photocatalysts and solar energy converters. 1 The characteristics of these devices, in which photogenerated carriers are used to trigger a chemical reaction or develop an electric potential, depend critically on the properties of charge transport. Indeed, for TiO 2 -based dye-sensitized solar cells, it has been demonstrated that the efficiency is typically limited by electron transport through TiO 2 nanostructures. 1,2 The issue of charge transport is also of considerable interest from the perspective of fundamental physics. TiO 2 , an ionic transition-metal oxide, exhibits strong electron-phonon coupling, resulting in low roomtemperature electron mobilities in the material. 3-5 However, despite its apparent importance, basic issues regarding charge transport in this material remain unclear. In particular, reported room-temperature electron Hall mobilities range from 0.01 to 10 cm 2 /V s. [3][4][5] In addition, the precise nature of the transport has remained unresolved. Because of the strong electron-phonon coupling in TiO 2 , electrons are described in terms of polarons, 6,7 quasiparticles consisting of an electron and accompanying lattice deformation. For a sufficiently strong electron-phonon interaction, small polarons are formed. This corresponds to the limit of localized, selftrapped electrons, and charge transport typically occurs through thermally activated hopping from one site to the next. Large polarons, with spatially extended wave functions, are formed for weaker coupling strength. They exhibit bandtype behavior, but with an enhanced mass relative to the band mass associated with an electron in a rigid lattice. Reports of the polaron mass in rutile range from 8m e to 190m e (m e is the free electron mass͒, 5,8 -11 and there have been conflicting arguments presented for the existence of small 5,6,12 and large 9,13 polarons in rutile. So although it is clear that the nature and efficiency of electron transport are determined by electron-phonon interactions that give rise to polaron formation and scattering events, the details of these interactions are unresolved.In this Rapid Communication, we investigate electronphonon interactions in single-crystal TiO 2 samples by means of frequency-dependent cond...

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Optical properties of large and small polarons and bipolarons

Cited by 428 publications

References 25 publications

Doping and temperature-dependent optical properties of oxygen-reducedBaTiO3−δ

Doping and temperature-dependent optical properties of oxygen-reducedBaTiO3−δ

Spectral properties of the 2D Holstein polaron

Electron transport inTiO2probed by THz time-domain spectroscopy

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