Raman Studies of Anisotropic Magnetic Excitations in Fluctuating Nematic Striped La2-xSrxCuO4 and the Comparison to Uniform Nd2-xCexCuO4

TL;DR

This study uses Raman scattering to investigate anisotropic magnetic excitations in fluctuating stripe-ordered La2-xSrxCuO4 and compares them to non-striped Nd2-xCexCuO4, proposing a model for superconductivity involving edge dislocations of charge stripes.

Contribution

It reveals the anisotropic magnetic excitations in stripe-ordered cuprates and proposes a novel model linking edge dislocations to superconducting pair formation.

Findings

Magnetic excitations show dispersion along and perpendicular to stripes.

Charge transfer occurs only perpendicular to stripes, aligned with edge dislocation Burgers vector.

Superconducting coherence length matches inter-charge stripe distance at x<0.2.

Abstract

The mechanism of the high temperature hole-doped superconductivity was investigated by Raman scattering. The Raman selection rule is unique, so that anisotropic magnetic excitations in a fluctuating spin-charge stripe can be detected as if it is static. We use different Raman selection rules for two kinds of magnetic Raman scattering processes, two-magnon scattering and high-energy electronic scattering. In order to confirm the difference, the Raman spectra of striped La2-xSrxCuO4 (LSCO) and non-striped Nd2-xCexCuO4 (NCCO) were compared. The main results in LSCO are (1) magnetic excitations are presented by individual energy dispersions for the k\parallel stripe and the k\perp stripe, (2) the charge transfer is allowed only in the direction perpendicular to the stripe. The direction is the same as the Burgers vector of an edge dislocation. Hence we assume that a charge moves together with the edge dislocation of the charge stripe. The superconducting coherence length is close to the inter-charge stripe distance at x < 0.2. Therefore we propose a model that superconducting pairs are formed in the edge dislocations. The binding energy is related to the stripe formation energy.