Browsing by Author "Bakr, M"
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- ItemElectronic and phononic Raman scattering in detwinned YBa2Cu3O6.95 and Y0.85Ca0.15Ba2Cu3O6.95: s-wave admixture to the d(x)(2)-y(2)-wave order parameter(America Physical Society, 2009-08-01) Bakr, M; Schnyder, AP; Klam, L; Manske, D; Lin, CT; Keimer, B; Cardona, M; Ulrich, CInelastic light (Raman) scattering has been used to study electronic excitations and phonon anomalies in detwinned, slightly overdoped YBa2Cu3O6.95 and moderately overdoped Y0.85Ca0.15Ba2Cu3O6.95 single crystals. In both samples modifications of the electronic pair-breaking peaks when interchanging the a and b axis were observed. The lineshapes of several phonon modes involving plane and apical oxygen vibrations exhibit pronounced anisotropies with respect to the incident and scattered light-field configurations. Based on a theoretical model that takes both electronic and phononic contributions to the Raman spectra into account, we attribute the anisotropy of the superconductivity-induced changes in the phonon lineshapes to a small s-wave admixture to the d(x)(2)-y(2) pair wave function. Our theory allows us to disentangle the electronic Raman signal from the phononic part and to identify corresponding interference terms. We argue that the Raman spectra are consistent with an s-wave admixture with an upper limit of 20%. © 2009, American Physical Society.
- ItemHighly anisotropic anomaly in the dispersion of the copper-oxygen bond-bending phonon in superconducting YBa2Cu3O7 from inelastic neutron scattering(American Physical Society, 2011-10-19) Raichle, M; Reznik, D; Lamago, D; Heid, R; Li, Y; Bakr, M; Ulrich, C; Hinkov, V; Hradil, K; Lin, CT; Keimer, BMotivated 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 similar to 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. © 2011, American Physical Society.
- ItemLong-range transfer of electron-phonon coupling in oxide superlattices(Australian Institute of Physics, 2013-02-06) Ulrich, C; Driza, AN; Blanco-Canosa, SA; Bakr, M; Soltan, S; Khalid, S; Mustafa, L; Kawashima, K; Christiani, G; Habermeier, HU; Khaliullin, G; Le Tacon, M; Keimer, BNot available
- ItemLong-range transfer of electron-phonon coupling in oxide superlattices(Nature Publishing Group, 2012-08-01) Driza, N; Blanco-Canosa, S; Bakr, M; Soltan, S; Khalid, M; Mustafa, L; Kawashima, K; Christiani, G; Habermeier, HU; Khaliullin, G; Ulrich, C; Le Tacon, M; Keimer, BThe electron-phonon interaction is of central importance for the electrical and thermal properties of solids, and its influence on superconductivity, colossal magnetoresistance and other many-body phenomena in correlated-electron materials is the subject of intense research at present. However, the non-local nature of the interactions between valence electrons and lattice ions, often compounded by a plethora of vibrational modes, presents formidable challenges for attempts to experimentally control and theoretically describe the physical properties of complex materials. Here we report a Raman scattering study of the lattice dynamics in superlattices of the high-temperature superconductor YBa2Cu3O7 (YBCO) and the colossal-magnetoresistance compound La2/3Ca1/3MnO3 that suggests a new approach to this problem. We find that a rotational mode of the MnO6 octahedra in La2/3Ca1/3MnO3 experiences pronounced superconductivity-induced line-shape anomalies, which scale linearly with the thickness of the YBCO layers over a remarkably long range of several tens of nanometres. The transfer of the electron-phonon coupling between superlattice layers can be understood as a consequence of long-range Coulomb forces in conjunction with an orbital reconstruction at the interface. The superlattice geometry thus provides new opportunities for controlled modification of the electron-phonon interaction in complex materials. © 2012, Nature Publishing Group.