Multiphonon generation during photodissociation of slow Landau-Pekar polarons

Journal Article · Wed Mar 15 04:00:00 EST 2006 · Journal of Experimental and Theoretical Physics

DOI:https://doi.org/10.1134/S1063776106030113· OSTI ID:21067720

Myasnikov, E N ^[1]; Myasnikova, A E ^[2]

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1. Rostov State Pedagogical University (Russian Federation)
2. Rostov State University (Russian Federation)

The spectra of the low-temperature photodissociation (photoionization) of Landau-Pekar polarons are calculated using the theory of quantum-coherent states and a new method of variation with respect to the parameters of phonon vacuum deformation. It is shown that the final polaron states upon photodissociation may have different numbers of phonons produced in a single dissociation event and different momenta of charge carriers. The spectrum of optical absorption related to the photodissociation of polarons exhibits a superposition of bands corresponding to various numbers of phonons formed as a result of dissociation of a single polaron. Due to a large width of the energy region corresponding to the final states of charge carriers, the halfwidth of each band is on the order of the energy of polaron coupling and is much greater than the phonon energy. For this reason, the individual phonon bands exhibit strong overlap. The very broad and, probably, structureless band formed as a result of the superposition of all these components begins at an energy equal to the sum of the polaron coupling energy (E{sub p}) and the phonon energy. This band has a maximum at a frequency of about 5.6E{sub p}/{Dirac_h} and a halfwidth on the order of 5.6E{sub p}/{Dirac_h} at a unit effective mass (m* = m{sub e}) of band electrons. For an effective charge carrier mass within m* = (1-3)m{sub e}, the energy of the polaron band maximum can be estimated as 5E{sub p} with an error of about 10%, and the halfwidth falls within 3.4E{sub p} < {Dirac_h}{omega}{sub 1/2} < 5.6E{sub p}. The multiphonon character of this band is related to a decay of the phonon condensate after the escape of charge carrier from a polaron. Such polarons are likely to be observed in the spectra of complex metal oxides, including high-temperature superconductors. Examples of such polaron bands in the reported absorption and photoconductivity spectra of nonstoichiometric cuprates, manganites, nickelates, and titanates are presented. A theory of the formation of Landau-Pekar polarons with the participation of branches of the polarization oscillations of the medium is developed. It is shown that, under certain conditions, such a multiphonon-dressed polaron can possess a coupling energy on the order of 0.2-0.3 eV, so that the maximum of the corresponding absorption band may occur at 1-1.5 eV.

• OSTI ID: 21067720
• Journal Information: Journal of Experimental and Theoretical Physics, Journal Name: Journal of Experimental and Theoretical Physics Journal Issue: 3 Vol. 102; ISSN JTPHES; ISSN 1063-7761
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION
ANNIHILATION OPERATORS
CHARGE CARRIERS
CUPRATES
DISSOCIATION
EFFECTIVE CHARGE
EFFECTIVE MASS
EIGENSTATES
HIGH-TC SUPERCONDUCTORS
NICKELATES
OXIDES
PHONONS
PHOTOCONDUCTIVITY
PHOTOIONIZATION
PHOTOLYSIS
POLARIZATION
POLARONS
TITANATES