Evidence for polaronic Fermi liquid in manganites

Alexandrov, A. S.; Zhao, Guo Meng; Keller, H.; Lorenz, B.; Wang, Y. S.; Chu, C. W.

doi:10.1103/physrevb.64.140404

Cited by 48 publications

(37 citation statements)

References 36 publications

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“…Hence, there is a large isotope effect on the carrier mass in polaronic metals, in contrast to the zero isotope effect in ordinary metals. Recently, this effect has been experimentally found in cuprates [42] and manganites [43]. With the increasing phonon frequency the 1/λ polaron expansion becomes valid for a smaller values of λ (see, for example, [28]).…”

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confidence: 97%

Breakdown of the Migdal-Eliashberg theory in the strong-coupling adiabatic regime

Alexandrov

2001

Europhys. Lett.

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In view of some recent works on the role of vertex corrections in the electron-phonon system we readress an important question of the validity of the Migdal-Eliashberg theory. Based on the solution of the Holstein model and 1/λ strongcoupling expansion, we argue that the standard FeynmanDyson perturbation theory by Migdal and Eliashberg with or without vertex corrections cannot be applied if the electronphonon coupling is strong (λ ≥ 1) at any ratio of the phonon, ω and Fermi, EF energies. In the extreme adiabatic limit (ω << EF ) of the Holstein model electrons collapse into self-trapped small polarons or bipolarons due to spontaneous translational-symmetry breaking at λ ≃ 1. With the increasing phonon frequency the region of the applicability of the theory shrinks to lower values of λ < 1.PACS numbers: 74.65.+n,74.60.Mj The theory of ordinary metals is based on 'Migdal's' theorem [1], which showed that the contribution of the diagrams with 'crossing' phonon lines (so called 'vertex' corrections) is small. This is true if the parameter λω/E F is small. It was then shown that if the adiabatic BornOppenheimer approach is properly applied to a metal, there is only negligible renormalisation of the phonon frequencies of the order of the adiabatic ratio, ω/E F << 1 for any value of λ [3]. The conclusion was that the standard electron-phonon interaction could be applied to electrons for any value of λ but it should not be applied to renormalise phonons [4]. As a result, many authors used the Migdal-Eliashberg theory with λ much larger than 1 (see, for example, Ref.[5]).However, starting from the infinite coupling limit, λ = ∞ and applying the inverse (1/λ) expansion technique [6] we showed [7][8][9] that the many-electron system collapses into small polaron regime at λ ∼ 1 almost independent of the adiabatic ratio. In this letter I compare the Migdal solution of the Holstein Hamiltonian with the exact one in the extreme adiabatic regime, ω/E F → 0, to show that the ground state of the system is a self-trapped insulating state with broken translational symmetry already at λ ≥ 1.The vertex corrections and the finite bandwidth are rather technical issues, playing no role in the extreme adiabatic limit [1,32,31]. There is, however, another basic assumption of the canonical Migdal-Eliashberg theory. That is the electron and phonon Green functions (GF) are translationally invariant. As a result one takes G(r, r ′ , τ ) = G(r− r ′ , τ ) with Fourier component G(k, Ω) prior to solving the Dyson equations. This assumption excludes the possibility of local violation of the translational symmetry due to the lattice deformation in any order of the Feynman-Dyson perturbation theory. This is similar to the absence of the anomalous (Bogoliubov) averages in any order of the perturbation theory. To enable electrons to relax into the lowest polaronic states, one has to introduce an infinitesimal translationally noninvariant potential, which should be set equal to zero only in the final solution for the GF [8]. As in the case of the...

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confidence: 97%

Breakdown of the Migdal-Eliashberg theory in the strong-coupling adiabatic regime

Alexandrov

2001

Europhys. Lett.

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“…More recently, the theory has been further confirmed experimentally. In particular, the oxygen isotope effect has been observed in the low-temperature resistivity of La 0:75 Ca 0:25 MnO 3 and Nd 0:7 Sr 0:3 MnO 3 and explained by CCDC with polaronic carriers in the ferromagnetic phase [16]. The current-carrier density collapse has been directly observed using the Hall data in La 0:67 Ca 0:33 MnO 3 and La 0:67 Sr 0:33 MnO 3 [17], and the first-order phase transition at T C , predicted by the theory [12], has been firmly established in the specific heat measurements [18].…”

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Phase Coexistence and Resistivity near the Ferromagnetic Transition of Manganites

2006

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Citation: ALEXANDROV, BRATKOVSKY and KABANOV, 2006 Pairing of oxygen holes into heavy bipolarons in the paramagnetic phase and their magnetic pair breaking in the ferromagnetic phase (the so-called current-carrier density collapse) has accounted for the first-order ferromagnetic-phase transition, colossal magnetoresistance, isotope effect, and pseudogap in doped manganites. Here we propose an explanation of the phase coexistence and describe the magnetization and resistivity of manganites near the ferromagnetic transition in the framework of the currentcarrier density collapse. The present quantitative description of resistivity is obtained without any fitting parameters, by using the experimental resistivities far away from the transition and the experimental magnetization, and is essentially model-independent.

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“…It revealed a fine phonon structure in the electron self-energy of the underdoped La 2−x Sr x CuO 4 samples [18], and a complicated isotope effect on the electron spectral function in Bi2212 [19]. Polaronic carriers were also observed in colossal magneto-resistance manganite including their lowtemperature ferromagnetic phase, where the isotope effect on the residual resistivity was measured and explained [20].…”

Section: Band-structure Isotope Effectmentioning

confidence: 90%

“…Actually, such effects have been observed in ferromagnetic oxides at low temperatures [20], and in cuprates [13,14,15]. To address ARPES isotope exponents [19] one has to calculate the electron spectral function A(k, E) taking into account phonon side-bands (i.e.…”

Section: Band-structure Isotope Effectmentioning

confidence: 99%

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High Temperature Superconductivity Due to a Long-Range Electron–Phonon Interaction, Application to Isotope Effects, Thermomagnetic Transport and Nanoscale Heterogeneity in Cuprates

Alexandrov

2005

J Supercond

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Evidence for polaronic Fermi liquid in manganites

Cited by 48 publications

References 36 publications

Breakdown of the Migdal-Eliashberg theory in the strong-coupling adiabatic regime

Breakdown of the Migdal-Eliashberg theory in the strong-coupling adiabatic regime

Phase Coexistence and Resistivity near the Ferromagnetic Transition of Manganites

High Temperature Superconductivity Due to a Long-Range Electron–Phonon Interaction, Application to Isotope Effects, Thermomagnetic Transport and Nanoscale Heterogeneity in Cuprates

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