Resonant soft x-ray scattering, stripe order, and the electron spectral function in cuprates

TL;DR

This paper reviews the use of resonant soft x-ray scattering (RSXS) to study stripe phenomena in cuprates, clarifies its relation to other spectral probes, and discusses future research directions involving high magnetic fields.

Contribution

It establishes that RSXS measures the squared modulus of an advanced Green's function, linking it more closely to STM than ARPES, and explores its potential in high magnetic field studies.

Findings

RSXS relates to the Green's function similar to STM.

RSXS has been used to study stripe order in various materials.

Future applications include high magnetic field studies of cuprates.

Abstract

We review the current state of efforts to use resonant soft x-ray scattering (RSXS), which is an elastic, momentum-resolved, valence band probe of strongly correlated electron systems, to study stripe-like phenomena in copper-oxide superconductors and related materials. We review the historical progress including RSXS studies of Wigner crystallization in spin ladder materials, stripe order in 214-phase nickelates, 214-phase cuprates, and other systems. One of the major outstanding issues in RSXS concerns its relationship to more established valence band probes, namely angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM). These techniques are widely understood as measuring a one-electron spectral function, yet a relationship between RSXS and a spectral function has so far been unclear. Using physical arguments that apply at the oxygen $K$ edge, we show that RSXS measures the square modulus of an advanced version of the Green's function measured with STM. This indicates that, despite being a momentum space probe, RSXS is more closely related to STM than to ARPES techniques. Finally, we close with some discussion of the most promising future directions for RSXS. We will argue that the most promising area lies in high magnetic field studies, particularly of edge states in strongly correlated heterostructures, and the vortex state in superconducting cuprates, where RSXS may clarify the anomalous periodicities observed in recent quantum oscillation experiments.