Hour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides.

Z W Li,U Rütt,A Ricci,J P Castellan,A C Komarek,O Gutowski,D Lamago,M Sprung,W Schmidt,M Rotter,A Piovano,O Sobolev,Y Drees

doi:10.1038/ncomms6731

Abstract

The magnetic excitations in the cuprate superconductors might be essential for an understanding of high-temperature superconductivity. In these cuprate superconductors the magnetic excitation spectrum resembles an hour-glass and certain resonant magnetic excitations within are believed to be connected to the pairing mechanism, which is corroborated by the observation of a universal linear scaling of superconducting gap and magnetic resonance energy. So far, charge stripes are widely believed to be involved in the physics of hour-glass spectra. Here we study an isostructural cobaltate that also exhibits an hour-glass magnetic spectrum. Instead of the expected charge stripe order we observe nano phase separation and unravel a microscopically split origin of hour-glass spectra on the nano scale pointing to a connection between the magnetic resonance peak and the spin gap originating in islands of the antiferromagnetic parent insulator. Our findings open new ways to theories of magnetic excitations and superconductivity in cuprate superconductors.

Highlights

The magnetic excitations in the cuprate superconductors might be essential for an understanding of high-temperature superconductivity
The spin excitations in high-temperature superconducting (HTSC) cuprates with a quasi two-dimensional layered crystal structure resemble an hour-glass if plotted as a function of energy and momentum transfer[1,2,3,4,5,6,7,8,9,10,11,12,13]
In our highly precise synchrotron measurements we were not able to detect any indications for charge stripe ordering reflections

Summary

Introduction

The magnetic excitations in the cuprate superconductors might be essential for an understanding of high-temperature superconductivity. Instead of the expected charge stripe order we observe nano phase separation and unravel a microscopically split origin of hour-glass spectra on the nano scale pointing to a connection between the magnetic resonance peak and the spin gap originating in islands of the antiferromagnetic parent insulator. We observe a fractal microstructure with a nanoscopic distribution of undoped and hole-doped regions indicating that hour-glass spectra consist of excitations with distinct origin on the nanometer scale. In our nanoscale phase separation scenario the energy of the neck of the hour-glass could be interpreted as the spin-gap within undoped islands of type of the antiferromagnetic parent insulator La2CoO4

Methods

Results

Conclusion