Doctoral Dissertations

Date of Award

8-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Norman Mannella, David Mandrus

Committee Members

Cristian Daniel Batista, Haidong Zhou

Abstract

Intercalation of transition metal dichalcogendies (TMDCs) by 3d-transition metals has been studied systematically. We mainly focus on intercalation into two host TMDCs 2H-NbS₂ and 2H-TaS₂ which are layered materials where the metal ions are in trigonal prismatic environment of chalcogens, the layers are separated by weak van der Waals force. So, foreign atoms or molecules can be inserted in between the layers of the TMDCs. The un-intercalated NbS₂ shows superconductivity below 6 K whereas TaS₂ exhibits coexistence of the superconductivity (Tc̳=0.8 K) with charge density wave phase (TC̳D̳W̳=75 K). In this research, the NbS₂ is intercalated by V atom with formula unit V₀.₃NbS₂, while TaS₂ by Cr with formula unit Cr₁/₃TaS₂. Upon the intercalation, the electronic as well as magnetic structure of host materials are likely to be modified. It is believed that the charge transfer between the 3d-intercalant and host TMDC, specifically the d-band of Nb or Ta, just causes an increase in chemical potential without altering the band structure and shape and size of Fermi surface, also known as rigid band model. And, the local moment in magnetic ion gives rise to magnetism via RKKY interaction. In order to examine the effect of intercalation in V₀.₃NbS₂ and Cr₁/₃TaS₂, we investigated the magnetic, transport, and electronic properties. In V₀.₃NbS₂, which crystallizes in P-31m space group, we observed canted antiferromag-netic (weak ferromagnetic) magnetic ordering with majority of charge carriers as hole type. From ARPES measurements, additional bands are appeared to cross the Fermi level and shape and size of the Fermi surface are modified as compared to NbS₂. Also, V-3d states are present near the Fermi level. These findings demonstrate that the simple rigid band picture is not viable in V₀.₃NbS₂ compound. Moreover, from the photon dependent ARPES measurements strong kz̳ dispersion is found in contrast to that of host NbS₂. Similarly, intercalated Cr₁/₃TaS₂ crystallizes in P6₃22 space group orders ferromagnetically. Surface structure is investigated by STM, LEED, and core level photoemmission experiments. The resonant photoemmission and ARPES measurements are performed to examine the effect of charge transfer between Cr and TaS₂ layer.

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