Synchrotron ARPES Studies Of The Band Structures Modulation Of Layered Materials

The Band structure is the kernel of solid materials.It is not only directly related to the electrical and optical properties that determine the application prospects of materials,but also intuitively reflects many microscopic interactions such as electron correlation,electron-phonon coupling,and spin splitting.Therefore,band engineering with band structure research and tailoring as the main content has always been a topic that has attracted much attention with theoretical and practical application values.Especially among a wide variety of layered materials,atomic intercalation,element substitution,stress regulation and thickness regulation have been developed according to their overall physical properties being dominated by the structure and properties of the basic unit layers and by the coupling modulation between the basic unit layers.However,considering the convenience of the experimental measurement of the band structure and the influence of the modulation methods,in this paper,we mainly choose two control methods:atomic intercalation and element substitution.Using synchrotron angleresolved photoemission spectroscopy(ARPES),a powerful experimental method that can directly observe the band structure in solid materials,combined with First principle calculation,electrical transport measurement,and crystal structure characterization,taking transition metal dichalcogenides and layered Iron-based superconductor CsFe2As2 as subjects to study the regulation of the effects of atomic intercalation and element substitution on the band structures.The electronic structure research of various systems involved in this thesis can not only effectively realize the precise tailoring of the band structure of parent materials,change its physical properties,and expand its application range,but also can provide experimental evidence for ascertaining how methods such as atomic intercalation and element substitution affect the intrinsic band structure of parent materials.The specific research work is divided into the following parts:1.Study on the band structure of metal element Re intercalated ZrSe2.ARPES was used to probe and compare the band structure of Re0.013ZrSe2 and ZrSe2,and it was found that the Re atoms introduced by intercalation provided extra electrons to the system,so that the unoccupied conduction band in ZrSe2 was gradually filled with electrons,thus triggering the phase transition of from semiconductor to metal.Meanwhile,the XRD data showed that the presence of Re atoms changed the interlayer spacing of the parent ZrSe2,but the overall band structure did not change significantly,showing a nearly rigid band shift.2.Study on the band structure of ZrSe2 substituted by Titanium.The band structures of a series of low substitution TixZr1-xSe2 samples were studied by ARPES,and it was found that the substitution of the same main group metal cation changed the bandgap size of the TixZr1-xSe2,making the system transition from a semiconductor to a metallic state.And the binding energy position of the top of the valence band shows a linear relationship with the doping amount of the Ti element.In addition,the detailed comparison of band structure shows that the spin-orbit splitting of the valence band also has a certain relationship with the doping amount of the Ti element.Combined with band calculations,we propose a reasonable explanation.3.Study on the band structure of magnetic element Cr intercalated CrTe2.The band structure of the room-temperature ferromagnet Cr1.3Te2 was directly observed by ARPES in this paper.By comparing with the parent CrTe2,we found that the intercalated Cr atoms provide additional electron carriers for the acceptor 1T-CrTe2,making the system transform into a semimetal.Moreover,the study also found that the ordered arrangement of spin did not significantly change the band structure.4.Study on the band structure of hole-doped Iron-based superconductor CsFe2As2.In the iron-based superconductor CsFe2As2,additional holes were introduced by replacing Fe atom with Cr atom,which made the system gradually transition from 3d5.5 to 3d5.ARPES characterization revealed that the Fermi surface symmetry of Cr-doped samples was changed,and explained the anomalous transport behavior of the Cr-doped samples compared to the parent CsFe2As2 from band structure perspective.Throughout the study,the Co-doped samples were treated as comparisons,demonstrating that the changes that occurred in the Cr-doped samples were not due to impurity or Fe atom vacancies.