Anisotropy in the thermal hysteresis of resistivity and charge density wave nature of single crystal SrFeO3-delta: X-ray absorption and photoemission studies

TL;DR

This study investigates the anisotropic resistivity and charge density wave behavior in SrFeO3-{delta} single crystals using temperature-dependent x-ray absorption and photoemission spectroscopy, revealing orbital and structural changes across thermal hysteresis.

Contribution

It provides new insights into the orbital and structural origins of anisotropic resistivity and charge density wave phenomena in SrFeO3-{delta} through combined spectroscopic and structural analysis.

Findings

Persistent out-of-plane orbitals during cooling

In-plane orbitals during warming below Tm

Band gap opening at low temperature indicating charge density wave

Abstract

The local electronic and atomic structures of the high-quality single crystal of SrFeO3-{delta} ({delta}~0.19) were studied using temperature-dependent x-ray absorption and valence-band photoemission spectroscopy (VB-PES) to investigate the origin of anisotropic resistivity in the ab-plane and along the c-axis close to the region of thermal hysteresis (near temperature for susceptibility maximum, Tm~78 K). All experiments herein were conducted during warming and cooling processes. The Fe L3,2-edge X-ray linear dichrois results show that during cooling from room temperature to below the transition temperature, the unoccupied Fe 3d eg states remain in persistently out-of-plane 3d3z2-r2 orbitals. In contrast, in the warming process below the transition temperature, they change from 3d3z2-r2 to in-plane 3dx2-y2 orbitals. The nearest-neighbor (NN) Fe-O bond lengths also exhibit anisotropic behavior in the ab-plane and along the c-axis below Tm. The anisotropic NN Fe-O bond lengths and Debye-Waller factors stabilize the in-plane Fe 3dx2-y2 and out-of-plane 3d3z2-r2 orbitals during warming and cooling, respectively. Additionally, a VB-PES study further confirms that a relative band gap opens at low temperature in both the ab-plane and along the c-axis, providing the clear evidence of the charge-density-wave nature of SrFeO3-{delta} ({delta}~ 0.19) single crystal.