Photoemission System with Polarized Hard X-rays for Probing Ground State Symmetry of Strongly Correlated Materials

TL;DR

This paper presents a polarized hard X-ray photoemission system designed to investigate the ground-state symmetry of strongly correlated materials, featuring advanced polarization control, low-temperature operation, and precise sample monitoring.

Contribution

The study introduces a novel HAXPES system with high polarization purity, low-temperature two-axis manipulation, and integrated sample monitoring, enabling detailed analysis of ground-state properties in complex materials.

Findings

Achieved a polarization degree of $-0.96$ with 98% vertical component.

Demonstrated polarized HAXPES on NiO revealing metallic spectral weight.

Operated at temperatures as low as 9 K for ground-state access.

Abstract

We have developed a polarized hard X-ray photoemission (HAXPES) system to study the ground-state symmetry of strongly correlated materials. The linear polarization of the incoming X-ray beam is switched by the transmission-type phase retarder composed of two diamond (100) crystals. The best degree of the linear polarization $P_L$ is $-0.96$, containing the vertical polarization component of 98%. A newly developed low temperature two-axis manipulator enables easy polar and azimuthal rotations to select the detection direction of photoelectrons. The lowest temperature achieved is 9 K, offering us a chance to access the ground state even for the strongly correlated electron systems in cubic symmetry. The co-axial sample monitoring system with the long-working-distance microscope enables us to keep measuring the same region on the sample surface before and after rotation procedures. Combining this sample monitoring system with a micro-focused X-ray beam by means of an ellipsoidal Kirkpatrick-Baez mirror (25 $\mu$m $\times$ 25 $\mu$m (FWHM)), we have demonstrated the polarized valence-band HAXPES on NiO for voltage application as resistive random access memories to reveal the origin of the metallic spectral weight near the Fermi level.