P16BL-7, BL-1

ARPES study of TiFexS2 (x = 0, 0.33)
Y. Nakashimaa, Y. Tanimotob, M. Sugimotob, H. Satoc, Y. Miyaib, S. Idetac,
K. Shimadac, M. Miyatad, M. KoyanodaFaculty of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
Graduate School of Advanced Science and Engineering, Hiroshima University,Higashi-Hiroshima 739-8526, Japanc
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, JapandSchool of Materials Science, Japan Advanced Institute of Science and Technology, Nomi 923-1292, Japanb

Keywords: intercalation, superlattice, angle resolved photoemission spectroscopy

1T-TiS2 is non-magnetic layered material with 1T-CdI2-type crystal structure. The hexagonal layer of Ti
ions is sandwiched between the two hexagonal layers of S ions and the Ti ion is octahedrally coordinatedwith six S ions. The S-Ti-S triple layers are covalently bonded and these TiS2 triple layers are weakly coupledwith van der Waals (vdW) force. In the vdW gap located between the TiS2 layers, the other 3d transitionmetal M can be intercalated as MxTiS2. Among them, FexTiS2 exhibits a wide variety of magnetic properties[1]. With increasing the Fe concentration from x = 0, the cluster spin grass (CG) state with the Ising spins isfound for x < 0.20. After exhibiting the antiferromagnetic (AFM) state up from x = 0.20 to 0.28, the CG stateis again realized for 0.28 < x < 0.38 and the AFM state for 0.38 < x < 0.50. Above x = 0.50, the ferrimagnetic
behavior is observed. On the other hand, the Fe ion intercalated in the vdW gap between the TiS2 layers
occupy the octahedral site surrounded by six S ions. X-ray studies reveal the Fe random distribution for x <0.20, while the formation of 2Ö3a ´ 2a ´ 2c or 2a ´ 2a ´ 2c superlattices due to the Fe ordering for x = 0.25
and Ö3a ´ Ö3a ´ 2c superlattice for x = 0.33. The rich magnetic states of FexTiS2 are expected to link to thechange in electronic band structure due to the Fe intercalation. In this study, we carried out angle-resolved
photoemission spectroscopy (ARPES) to reveal the electronic band structure of FexTiS2 (x = 0, 0.33) atbeamlines BL-1 and BL-7 of Hiroshima Synchrotron Radiation Center (HSRC).
$ directions ofFigure 1(a) shows the ARPES intensity plots of TiS2 measured at hv=66 eV along the Γ"-Mthe surface Brillouin zone, roughly corresponding to G-M direction of the bulk Brillouin zone, estimatedfrom the hv-dependent measurements. We find an electron pocket derived from the Ti 3d states around theM point. Almost non-dispersive band is observed at binding energy of EB = 0.3 eV, which is assigned to the3d states of the Ti ions self-intercalated in the vdW gap between TiS2 layers. The parabolic band aroundthe G point is due to the S 3p states.

% direction.
FIGURE 1. ARPES intensity plots of (a) TiS2 and (b) Fe0.33TiS2 measured at hn = 66 eV along Γ#-M

Figure 1(b) shows the ARPES intensity plots of Fe0.33TiS2. The electron pocket around the M point isshifted to higher binding energy. In addition, the parabolic S 3p band is also shifted. These results indicatethat electrons are transferred from the intercalated Fe ions to host TiS2 layers. The dispersive Fe 3d-derived
band is observed around EB = 0.3 - 0.7 eV, reflecting the Fe ions align periodically in the vdW gap parallelto the TiS2 layers (in plane). The Fe 3d band seems to be bent upward before the M point, probably due tothe Ö3a ´ Ö3a periodicity in plane for x = 0.33. We measured the ARPES spectra along the G-A direction
with changing hv from 30 to 124 eV. We find that the Fe 3d band exhibits the dispersion along the direction
normal to the TiS2 layers and has half period of the S 3p band, reflecting the 2c periodicity due to theformation of Ö3a ´ Ö3a ´ 2c superlattice.

REFERENCES
1. N. V. Selezneva, E. M. Sherokalova, A. Podlesnyak, M. Frontzek and N. V. Baranov, Phys. Rev. Mater. 7, 014401 (2023).