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Abstract: Stripe order where electrons self-organize into alternating periodic charge-rich and magnetically-ordered charge-poor parallel lines was proposed as a way of optimizing the kinetic energy of holes in a doped Mott insulator. Static stripes detected as extra peaks in diffraction patterns, appear in a number of oxide perovskites as well as some other systems. The more controversial dynamic stripes, which are not detectable by diffraction, may be universally present in copper oxide superconductors. Thus it is important to learn how to detect dynamic stripes as well as to understand their influence on electronic properties. This review article focuses on lattice vibrations (phonons) that might show signatures of the charge component of dynamic stripes. The first part of the article describes recent progress in learning about how the phonon signatures of different types of electronic charge fluctuations including stripes can be distinguished from purely structural instabilities and from each other. Then I will focus on the evidence for dynamic stripes in the phonon spectra of copper oxide superconductors. [Copyright &y& Elsevier]

Motivated by predictions of a substantial contribution of the "buckling" vibration of the CuO2 layers to d-wave superconductivity in the cuprates, we have performed an inelastic neutron scattering study of this phonon in an array of untwinned crystals of YBa2Cu3O7. The data reveal a pronounced softening of the phonon at the in-plane wave vector q = (0, 0.3) upon cooling below ~105 K, but no corresponding anomaly at q = (0.3, 0). Based on the observed in-plane anisotropy, we argue that the electron-phonon interaction responsible for this anomaly supports an electronic instability associated with a uniaxial charge-density modulation and does not mediate d-wave superconductivity. [ABSTRACT FROM AUTHOR]

Abstract: Inelastic X-ray scattering (IXS) was used to study the Cu–O bond-stretching vibrations in the static stripe phase compound La1.48Nd0.4Sr0.12CuO4. It was found that the intrinsic width in Q-space of the previously reported huge anomalous phonon softening and broadening is approximately 0.08r.l.u. HWHM. A detailed comparison was also made to inelastic neutron scattering (INS) studies, which indicate a two-peak lineshape (with superimposed broad and narrow peaks) in the vicinity of the anomaly. The high resolution IXS data show that the narrow peak is mostly an artifact of the poor transverse Q-resolution of INS. Otherwise, the agreement between the INS and IXS was excellent. [Copyright &y& Elsevier]

The attempt to understand copper oxide superconductors is complicated by the presence of multiple strong interactions in these systems. Many believe that antiferromagnetism is important for superconductivity, but there has been renewed interest in the possible role of electron–lattice coupling. The conventional superconductor MgB2 has a very strong electron–lattice coupling, involving a particular vibrational mode (phonon) that was predicted by standard theory and confirmed quantitatively by experiment. Here we present inelastic scattering measurements that show a similarly strong anomaly in the Cu–O bond-stretching phonon in the copper oxide superconductors La2-xSrxCuO4 (with x = 0.07, 0.15). Conventional theory does not predict such behaviour. The anomaly is strongest in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4, compounds that exhibit spatially modulated charge and magnetic order, often called stripe order; it occurs at a wave vector corresponding to the charge order. These results suggest that this giant electron–phonon anomaly, which is absent in undoped and over-doped non-superconductors, is associated with charge inhomogeneity. It follows that electron–phonon coupling may be important to our understanding of superconductivity, although its contribution is likely to be indirect. [ABSTRACT FROM AUTHOR]

The susceptibility of thin superconductor film was obtained. The absorption of energy of external electromagnetic field by superconductor film located at a semiconductor substrate was calculated. A new approach to calculation of the dispersion relation for eigenmodes of a strong inhomogeneous system was developed. The dispersion relations of eigenmodes of a superconductor thin film on the semiconductor substrate was calculated using the developed approach. [ABSTRACT FROM AUTHOR]

Arising from: F. Giustino, M. L. Cohen & S. G. Louie 452, 975–978 (2008)One of the possible mechanisms of high transition temperature (Tc) superconductivity is Cooper pairing with the help of bosons, which change the slope of the electronic dispersion as observed by photoemission. Giustino et al. calculated that in the high temperature superconductor La1.85Sr0.15CuO4 crystal lattice vibrations (phonons) should have a negligible effect on photoemission spectra and concluded that phonons do not have an important role. Here we show that the calculations used by Giustino et al. do not reproduce the huge influence of electron–phonon coupling on important phonons observed in experiments. Thus, we would similarly expect that these calculations do not explain the role of electron–phonon coupling for the electronic dispersion. [ABSTRACT FROM AUTHOR]

Abstract: Inelastic neutron scattering was used to search for an influence of superconductivity on the phonons in optimally doped and in slightly overdoped Ba(Fe1− x Co x )2As2, x =0.06 and x =0.10. The study focused on phonons with energies close to the superconducting gap energy 2Δ because it is well known that such phonons will respond most strongly to the opening of the gap. We were able to obtain high quality data but nevertheless, we could not detect any influence of superconductivity on the phonons, neither on the linewidths nor on the frequencies. Our results imply that any coupling of low energy phonons to the electrons has to be very small, much smaller than observed in conventional superconductors with a high T c. Our results are in line with the low coupling strength predicted by density functional theory for the investigated phonon branches. [Copyright &y& Elsevier]

We report inelastic neutron-scattering experiments on RNi2B2C single crystals (R=Tb and Ho) to investigate the dispersion of low-energy phonons. Both compounds order antiferromagnetically at low temperatures. For superconducting HoNi2B2C we observe a strong softening of two phonon branches similar to other superconducting RNi2B2C compounds. In contrast, for the non-superconducting TbNi2B2C we could not detect significant changes in the phonon spectra as a function of temperature. This correlation between superconductivity and the observed phonon softening indicates a strong electron–phonon interaction and strongly supports the BCS-like description of these compounds. [Copyright &y& Elsevier]

In superconducting copper oxides, some Cu-O bond-stretching phonons around 70 meV show anomalous giant softening and broadening of electronic origin, and electronic dispersions have large renormalization kinks near the same energy. These observations suggest that phonon broadening originates from quasiparticle excitations across the Fermi surface and the electronic dispersion kinks originate from coupling to anomalous phonons. Wemeasured the phonon anomaly in underdoped (x = 0.05) and overdoped (x = 0.20 and 0.25) La2-xSrxCuO4 by inelastic neutron and x-ray scattering with high resolution. Combining these and previously published data, we found that doping dependence of the magnitude of the giant phonon anomaly is very different from that of the ARPES kink, i.e., the two phenomena are not connected. We show that these results provide indirect evidence that the phonon anomaly originates from novel collective charge excitations as opposed to interactions with electron-hole pairs. Their amplitude follows the superconducting dome so these charge modes may be important for superconductivity. [ABSTRACT FROM AUTHOR]

The Fe1+yTe1-xSex compounds belong to the family of iron-based high-temperature superconductors, in which superconductivity often appears upon doping antiferromagnetic parent compounds. Unlike other Fe-based superconductors (in which the antiferromagnetic order is at the Fermi-surface nesting wave vector [½,½,1]), Fe1+yTe orders at a different wave vector, [½,0,½]. Furthermore, the ordering wave vector depends on y, the occupation of interstitial sites with excess iron; the origin of this behavior is controversial. Using inelastic neutron scattering on Fe1.08Te, we find incommensurate magnetic fluctuations above the Néel temperature, even though the ordered state is bicollinear and commensurate with gapped spin waves. This behavior can be understood in terms of a competition between commensurate and incommensurate order, which we explain as a lock-in transition caused by the magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Nematicity is ubiquitous in electronic phases of high-Tc superconductors, particularly in the Fe-based systems. We used inelastic x-ray scattering to extract the temperature-dependent nematic correlation length ξ from the anomalous softening of acoustic phonon modes in FeSe, underdoped Ba(Fe0.97Co0.03)2As2, and optimally doped Ba(Fe0.94Co0.06)2As2. In all cases, we find that ξ is well described by a power law (T-T0)-1/2 extending over a wide temperature range. Combined with the previously reported Curie-Weiss behavior of the nematic susceptibility, these results point to the mean-field character of the nematic transition, which we attribute to a sizable nematoelastic coupling that is likely detrimental to superconductivity. [ABSTRACT FROM AUTHOR]