# Resonant soft x-ray scattering from stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ detected by a transition edge sensor array detector

## TL;DR

This study demonstrates that transition edge sensor detectors significantly reduce fluorescence background in resonant soft x-ray scattering, enabling clearer detection of weak or diffuse valence band order signals in complex materials.

## Contribution

The paper introduces the use of TES detectors in RSXS to mitigate fluorescence background, improving data quality and opening new possibilities for studying fluctuating or glassy orders.

## Key findings

- TES detectors reject fluorescence background at suitable detuning
- Data quality improves 5 to 10 times with TES compared to energy-integrated methods
- Potential to discover new valence band phenomena in complex materials

## Abstract

Resonant soft x-ray scattering (RSXS) is a leading probe of valence band order in materials best known for detecting charge density wave order in the copper-oxide superconductors. One of the biggest limitations on the RSXS technique is the presence of a severe fluorescence background which, like the RSXS cross section itself, is enhanced under resonant conditions. This background prevents the study of weak signals such as diffuse scattering from glassy or fluctuating order that is spread widely over momentum space. Recent advances in superconducting transition edge sensor (TES) detectors have led to major improvements in energy resolution and detection efficiency in the soft x-ray range. Here, we perform a RSXS study of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ at the Cu $L_{3/2}$ edge (932.2 eV) using a TES detector with 1.5 eV resolution, to evaluate its utility for mitigating the fluorescence background problem. We find that, for suitable degree of detuning from the resonance, the TES rejects the fluorescence background, leading to a 5 to 10 times improvement in the statistical quality of the data compared to an equivalent, energy-integrated measurement. We conclude that a TES presents a promising approach to reducing background in RSXS studies and may lead to new discoveries in materials exhibiting valence band order that is fluctuating or glassy.