Infrared signatures of hole and spin stripes inLa2−xSrxCuO4

Abstract

We investigate the hole and lattice dynamics in a prototypical high temperature superconducting system La2−xSrxCuO4 using infrared spectroscopy. By exploring the anisotropy in the electronic response of CuO2 planes we show that our results support the notion of stripes. Nevertheless, charge ordering effects are not apparent in the phonon spectra. All crystals show only the expected infrared active modes for orthorhombic phases without evidence for additional peaks that may be indicative of static charge ordering. Strong electron-phonon interaction manifests itself through the Fano lineshape of several phonon modes. This analysis reveals anisotropic electron-phonon coupling across the phase diagram, including superconducting crystals. Due to the ubiquity of the CuO2 plane, these results may have implications for other high Tc superconductors.The nature of spin and/or charge stripes in the cuprates and their involvement to high temperature superconductivity are currently at the center of a debate in condensed matter physics.[1] The expression "stripes" is a general term indicating that spins and/or holes may arrange themselves in quasi-one dimensional, or more complicated self-organized patterns. The stripe-ordered state minimizes the energy of holes doped in an antiferromagnetic matrix thus leading to new inhomogeneous state of matter.[2] Static one-dimensional (1D) charge stripes have been observed in the La 2−x−y Nd y Sr x CuO 4 (LNSCO) system[3] with complimentary evidence from neutron and x-ray diffraction techniques. Although signatures of stripes by way of charge ordering have not been observed in La 2−x Sr x CuO 4 (LSCO) and other high temperature superconductors, there is evidence of the possible existence of dynamical stripes in these systems. [4] On the other hand, spin stripes have been discovered in LSCO[5] and many researchers agree upon their universality in high-T c superconductors. However a key issue regarding this new electronic state of matter concerns the role of stripes in relation to superconductivity, i.e. whether they are responsible for high temperature superconductivity or a competing phase with it.Signatures of quasi one dimensional behavior should be observable in optical spectroscopy. In particular the lowering of symmetry due the formation of rigid charge density waves results is known to have dramatic implications for infrared (IR) active phonons.[6] Electronic 1D behavior can be directly probed by way of frequency dependent conductivity. An observation of the anisotropic conductivity in weakly doped LSCO is consistent with the notion of stripes [7,8]. Notably these observations imply deviations from a hypothetical model in which the stripes are rigid rivers of charge embedded within an antiferromagnetic background. Moreover, electronic and lattice fingerprints of 1D transport have not been systematically explored as a function of doping. The goal of this work is to apply infrared spectroscopy for the purpose of a detailed examination of spin/charge ordering effects in a series of ...

Superconducting pairing and the pseudogap in the nematic dynamical stripe phase of La2−xSrxCuO4

“…13(b). The satellite peak is also infrared active 134 . The regular stripe structure has the inversion symmetry, but the edge dislocation in Fig.…”

“…18. The sharp peak does not appear in the infrared spectra, but the satellite peak appears 134 . The intensity of the sharp peak moves into the satellite peak as carrier density increases.…”

An Intrinsic Bond-Centered Electronic Glass with Unidirectional Domains in Underdoped Cuprates

“…Powder neutron diffraction reveals related local lattice distortions (21) and optical spectroscopy the anomalous anisotropic conductivity and electron-phonon couplings (27 …”

Theory of anisotropic hopping transport due to spiral correlations in the spin-glass phase of underdoped cuprate superconductors

“…3 Recent infrared experiments that carefully identify phonon modes in LSCO once again find no charge ordering tendencies in the spin-glass phase of this material. 17 Therefore we take the point of view that the ground state has a spiral spin structure, and calculate the transport anisotropy in the variable-range hopping (VRH) regime for low temperature and frequency, where the anisotropy has the largest value. We show that the spatial anisotropy of the hole wave-function in a spiral translates into anisotropy of the hopping transport.…”