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Soft-x-ray ARPES at BACH

Polarization-dependent soft-x-ray ARPES (SX-ARPES) has been performed at the BACH beamline to study the electronic structure of the chiral helimagnet Cr1/3NbS2.

N. Sirica et al. Physical Review B, Vol. 94 - N, pp. 075141 (2016) doi: 10.1103/PhysRevB.94.075141

The electronic structure of the chiral helimagnet (CHM) Cr1/3NbS2 has been studied with core level (PES) and angle-resolved photoemission spectroscopy (ARPES).  The surface of Cr1/3NbS2 exposed by in-situ cleaving possesses a stoichiometry and an atomic ordering that is different from that in the bulk.  Specifically, the surface consists of S terminated regions with periodic order, with residual Cr atoms not periodically ordered.  The residual Cr atoms randomly distributed on the surface have been identified with resonant-PES as the origin of the non-dispersing states located » 0.5 – 2 eV below EF observed in ARPES data taken with photons of 40 eV and 48 eV.  Despite the presence of disordered areas on the surface, the ARPES data are of high quality, and reveal the presence of dispersing bands.  Low energy electron diffraction (LEED) images exhibit intense spots corresponding to the 1×1 periodicity of the NbS2 lattice, and (√3×√3)R(30°) superstructure spots of weaker intensity originating from sub-surface ordering of the Cr atoms with the same periodicity as in the bulk.  The ARPES data appear to be consistent with the results of the more bulk sensitive soft x-ray ARPES (SX-ARPES) experiments carried out at higher photon energies.  Differences between the data taken at different photon energies are more easily explained as a result of the variation of the matrix elements, rather than suggesting intrinsic major differences of the electronic structures representative of different probing depths.  Even though the Cr atoms on the surface of Cr1/3NbS2 are disordered and occupy sites with a lower symmetry, salient features of the electronic structure revealed by low energy ARPES, such as band dispersion and Fermi momenta, are not significantly modified as compared to the bulk.  Further confirmation of this statement derives from the observation of a band replica at the G point of the bands found at the K point in both conventional ARPES and SX-ARPES experiments.  The possibility of observing band replicas at the G point is a direct consequence of the superlattice potential due to the (√3×√3)R30° superstructure of the Cr atoms in the bulk.    

 

 

The electronic structure of the chiral helimagnet Cr1/3NbS2 appears to be far more complex and intriguing than anticipated.  The results and similar studies of this type, are likely to be important in order to provide insights into the connection between the electronic structure and the functional properties of chiral helimagnets, spin-textures and spin orbit interaction effects in magnetic multilayers and magnetic thin films, and to develop a systematic understanding as to how intercalation with 3d magnetic atoms serves to modify the electronic structure of the host material in potential technological applications of layered TMDCs.

Electronic structure of the chiral helimagnet and 3d-intercalated transition metal dichalcogenide Cr1/3NbS2 
Sirica N., Mo S-., Bondino F., Píš I., Nappini S., Vilmercati P., Yi J., Gai Z., Snijders P.C., Das P.K., Vobornik I., Ghimire N., Koehler M.R., Li L., Sapkota D., Parker D.S., Mandrus D.G., Mannella N. 
Physical Review B, Vol. 94 - N, pp. 075141 (2016) 
doi: 10.1103/PhysRevB.94.075141



 

Last Updated on Wednesday, 12 December 2018 12:58