Magnetic Field Effect and Phonon Anomalies in 214 La-based Cuprates.*

ABSTRACT.
The competition between superconductivity and electronic periodicities is a central theme in condensed matter physics, since it has shed light into the complexity of the phase diagram of cuprates. Understanding this relationship with other Fermi surface instabilities is essential to develop a satisfactory theory of superconductivity.
214 La-based cuprates [1], YBa₂Cu₃O_6+δ (YBCO) and related compounds exhibit a momentum and field dependence of short ranged, weakly correlated charge periodicities (Charge Density Wave, CDW) for doping levels 0.08≤p≤0.15 [2]. Here, I will present Resonant X Ray Scattering measurements at the Cu L- and O K-edges that indicate a strong stability of the stripe order in the Low Temperature Tetragonal (LTT) phase. In addition, Inelastic X Ray Scattering shows a softening and broadening of the low energy acoustic phonon at Q_CO below the superconducting temperature T_C. The data indicate a strong influence of the lattice symmetry and e-ph coupling in the stabilization of the charge stripe order and reveals nesting properties of the Fermi surface [3].
References
[1] J. M. Tranquada et al. Nature 375, 561 (1995).
[2] G. Ghiringhelli et al. Science 337, 821 (2012).
[3] S. Blanco-Canosa et al. in preparation.