Chirality switching in 1T -TaS2 induced by highly charged ion irradiation

Abstract

It was recently shown that slow highly charged ions (HCIs) can perforate single two- dimensional layers in a van-der-Waals stack [1]. The ultimate surface sensitivity in atomic- scale defect formation of this class of ions stems from the very localized, highly efficient interaction of the HCI with the electronic sub-system of a material [2]. Strong electronic excitations then couple to lattice atomic motion, causing formation of defects or pores. As the surface electronic state is the determining factor for the susceptibility for nanostructure formation from strong electronic excitations in general, we use 1T-TaS2, a prototypical charge- density-wave phase material. 1T-TaS2 undergoes a series of phase transitions from a metallic state to a Mott insulating state and provides therefore a platform to test HCI-induced defect formation scenarios with the same material, only varying the electronic properties. We monitor ion-induced defect formation in operando by angle-resolved photoelectron spectroscopy (ARPES) using 400 eV soft X-rays with fixed helicity, provided from the PETRA III synchrotron at DESY. Figure 1 (see printed version) shows ARPES maps at specific energies before and after a total Xe8+ ion fluence of 9x1011/cm2 at 22.5 keV kinetic energy was applied to bulk 1T-TaS2 at 50K (commensurate charge-density-wave Mott insulator phase). One can clearly see that the ARPES map changes the intensity distribution and the difference plot in (c) and (g) indicate that the intensity redistributes according to a mirroring across the Γ-M direction. In this contribution I will discuss defect mechanisms driving a surface chirality switch from HCIs at low ion fluencies, where surface amorphization is still negligible.