The aim of this work is an experimental study of the electronic interaction in the BiTeCl compound and its effect on the formation of the electronic structure. The used method of resonant x-ray photoemission spectroscopy (RPES) allows distinguishing the contributions of the various components to the valence bands. We can study not only the ground state, but also the characteristics of excited two-particle states, the reaction to external action, and the relaxation processes of the electronic system.
BiTeCl has a hexagonal crystal structure of alternating layers of chlorine, bismuth and tellurium atoms. The crystal has no inversion symmetry due to the continuous stacking order of the three atomic layers. The weak bonding between the Te and Cl layer provides a natural cleaving plane in the (0001) plane. The BiTeCl crystal was grown based on BiCl3–Bi2Te3. The telluride compound was obtained by fusing stoichiometric amounts of elemental Bi and Te at 600 ◦C. BiCl3 was prepared by the evaporation of a saturated solution of Bi2O3 in HCl acid. The charge was then sealed in a growth quartz ampoule under a pressure of 10−3 Torr. After heating to 430 ◦C at a rate of 20 ◦C h−1 followed by 1 day of soaking at this temperature the melt was crystallized by a modified Bridgman method . According to our x-ray diffraction analysis a major part of the aggregate consisted of the BiTeCl phase, which was selected for the RPES measurements.
The experiments were carried out at the Russian–German laboratory of the BESSY II synchrotron (Berlin). The RPES spectra were obtained using synchrotron radiation with 150–900 eV photon energy range. The energy resolution was 0.1 eV. The perfect working surface was prepared by cleaving the samples directly in the ultrahigh vacuum chamber of the spectrometer. The main regularities that appear when the excitation energy and the photoionization cross-section change were established.
The reported study was funded by RFBR, project number 19-29-12061 and was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme “Spin” No. АААА-А18-118020290104-2 and АААА-А19-119081990020-8).