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Pintschovius, L.; Reichardt, W.; Kläser, M.; Wolf, Th.; Löhneysen, H. v.

doi:10.1103/physrevlett.89.037001

Cited by 50 publications

(50 citation statements)

References 17 publications

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“…Finally, inelastic neutron scattering experiments pointed to an anomalous behavior in the dispersion of the in-plane longitudinal optical phonons with wave vectors [0, 0.25, 0] in the YBCO superconductors. This corresponds to bond stretching vibrations being associated with dynamical charge fluctuations on the Cu ions driven by the displacement of the neighboring ligand environment of the O atoms 6 .…”

Section: Introductionmentioning

confidence: 99%

Resonant pairing isotope effect in polaronic systems

Ranninger

Romano²

2005

Phys. Rev. B

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The intermediate coupling regime in polaronic systems, situated between the adiabatic and the anti-adiabatic limit, is characterized by resonant pairing between quasi-free electrons which is induced by an exchange interaction with localized bipolarons. The onset of this resonant pairing takes place below a characteristic temperature T * and is manifest in the opening of a pseudogap in the density of states of the electrons. The variation of T * is examined here as a function of (i) the typical frequency ω0 of the local lattice modes, which determines the binding energy of the bipolarons, and (ii) the total concentration of charge carriers ntot = nF + nB, where nF and nB are the densities of free electrons and bipolarons, respectively. The variation of either of these quantities induces similar changes of the value of nB with respect to that of nF , in this way leading to a shift of T * . For finite, but small values of nB (≤ 0.1 per site), we find negative and practically doping independent values of the corresponding isotope coefficient α * . Upon decreasing ntot such that nB becomes exponentially small, we find a rapid change in sign of α * . This is related to the fact that the system approaches a state which is more BCS-like, where electron pairing occurs via virtual excitations into bipolaronic states and where T * coincides with the onset of superconductivity.

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Section: Introductionmentioning

confidence: 99%

Resonant pairing isotope effect in polaronic systems

Ranninger

Romano²

2005

Phys. Rev. B

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“…It is interesting to note that this anisotropy matches the one previously observed in the anomalous dispersion of copper-oxide phonon modes in YBCO 6+δ . [42][43][44] Measurements of YBCO 6.55 and YBCO 6.6 crystals under the same experimental conditions further allowed us to compare the overall intensities of the incommensurate peaks in both crystals. The peak along K is about ∼ 25% less intense in YBCO 6.55 than it is in YBCO 6.6 ; the intensity difference along H is correspondingly larger.…”

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confidence: 99%

Momentum-Dependent Charge Correlations inYBa2Cu3O6+δSuperconductors Probed by Resonant X-Ray Scattering: Evidence for Three Competing Phases

et al. 2013

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We have used resonant x-ray scattering to determine the momentum dependent charge correlations in YBa2Cu3O6.55 samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments were carried out on a YBa2Cu3O6.6 crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length were found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa2Cu3O 6+δ .PACS numbers: 74.20. Rp, 74.25.Gz, 74.25.Kc, 74.72.Bk High-temperature superconductivity in the cuprates arises from doping of charge carriers into Mott-insulators with antiferromagnetically ordered CuO 2 planes.[1] At sufficiently high density, the carriers screen out the random potential created by the donor or acceptor atoms and generate a uniform metallic state out of which superconductivity arises. In underdoped cuprates, however, the screening is less effective, and the role of materialsspecific disorder in the formation of the unusual spin and/or charge textures observed in this regime of the phase diagram has been a subject of long-standing debate. [2-16] Recent research on the stoichiometric underdoped compounds YBa 2 Cu 3 O 6.5 and YBa 2 Cu 4 O 8 has provided new perspectives for the resolution of the influence of disorder on the electronic phase behavior of the underdoped cuprates. In these materials, the oxygen acceptors are arranged in ordered chains rather than placed randomly in the crystal lattice, so that chemical and structural disorder is minimized.[17] The results of recent quantum oscillation experiments [18][19][20] in high magnetic fields indicate a reconstruction of the Fermi surface by a long-range electronic superstructure. [21][22][23] This discovery has sparked another intense debate on the nature of the high-field ordering and its relation to the "pseudogap" observed in these and other underdoped cuprates [24] above the superconducting transition temperature, T c , in the absence of external fields. The pseudogap, in turn, is intimately related to the superconducting gap, and an explanation of its origin is considered an essential element of any theory of high-temperature superconductivity.Whereas research on YBa 2 Cu 4 O 8 has been limited, because only small crystals are available and the doping level cannot be varied in a straightforward manner, YBa 2 Cu 3 O 6.5 is a member of the extensively studied YBa 2 Cu 3 O 6+δ (YBCO 6+δ , 123) family, where the concentration of mobile holes in the CuO 2 layer...

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“…Whereas the corresponding breathing mode at (π, π) shows much smaller softening and no anomalous broadening (Fig.5). This effect appears to be generic for cuprates and detailed neutron scattering studies have been reported for La 2−x Sr x CuO 4 [18,19,20,21], YBa 2 Cu 3 O 6+x [19,22,23] and also for Bi-based cuprates [24]. This certainly shows that there are phonons which couple rather strongly to the charge carriers that contribute to superconductivity, and one may ask what is special about the interaction of strongly correlated electrons and phonons.…”

Section: Renormalization Of Breathing Phononsmentioning

confidence: 76%

Charge dynamics of t-J model and anomalous bond-stretching phonons in cuprates

Horsch¹,

Khaliullin²

2003

AIP Conference Proceedings

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Abstract. The density response of a doped Mott-Hubbard insulator is discussed starting from the t-J model in a slave boson 1/N representation. In leading order O(1) the density fluctuation spectra N(q, ω) are determined by an undamped collective mode at large momentum transfer, in striking disagreement with results obtained by exact diagonalization, which reveal a very broad dispersive peak, reminescent of strong spin-charge coupling. The 1/N corrections introduce the polaron character of the bosonic holes moving in a uniform RVB background. The resulting N(q, ω) captures all features observed in diagonalization studies, fulfills the appropriate sum rules, and apart from the broadening of the collective mode shows a new low energy feature at the energy χJ + δt related to the polaron motion in the spinon background. It is further shown that the low energy structure, which is particularly pronounced in (π, 0) direction, describes the strong renormalization and anomalous damping of the highest bond-stretching phonons in La 2−x Sr x CuO 4 .

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Pronounced In-Plane Anisotropy of Phonon Anomalies inYBa2Cu3O6.6

Cited by 50 publications

References 17 publications

Resonant pairing isotope effect in polaronic systems

Resonant pairing isotope effect in polaronic systems

Momentum-Dependent Charge Correlations inYBa2Cu3O6+δSuperconductors Probed by Resonant X-Ray Scattering: Evidence for Three Competing Phases

Charge dynamics of t-J model and anomalous bond-stretching phonons in cuprates

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