Engineering Electronic Properties Of Layered Two-dimensional Single-Crystal Materials And Their Synchrotron Radiation-based Studies

Engineering the intrinsic electronic properties of two dimensional(2D)layered materials to reveal new and exotic properties for utilization in various realistic applications is an active area of research in condensed matter physics.In this thesis,we utilized physical method such as strain and chemical methods like atoms intercalation and doping to engineer the electronic properties of some selected layered materials.Density Functional theory calculations was used to guide our choice of atoms and insight to selecting appropriate experimental methods for the materials.We predicted new exotic electronic properties through this method,then utilized experimental methods to engineer and confirm some of the as-predicted properties by synthesis.The electronic,chemical and structural properties were characterized using low-temperature transport experiments and using synchrotron radiation-based characterizations.In the first study.we engineered the electronic,and optical properties of a layered ternary transition metal chalcogenide ZrGeTe4 monolayer using strain.2D ZrGeTe4 crystal is a semiconductor,exhibiting anisotropic elastic and optical response.Application of external compression or tensile strain can modulate its bandgap and its optical absorption edge.In particular,a semiconductor-to-metal transition was observed in the ZrGeTe4 monolayer under a compressional strain.The flexibility and significantly strain-tunable electronics properties in the 2D ZrGeTe4 monolayer render it functional in nanoscale electronic and optoelectronic applicationsIn the second study,utilizing first-principles calculations,we predicted an enhanced superconducting transition,and topological nodal lines features,with drumhead-like shaped surface states protected by inversion symmetry in the Sn intercalated TaSe2.Using the Chemical vapor transport technique,we synthesized Sn0.5TaSe2 single-crystals.Through low temperature experiment on the as-synthesized single-crystals,we corroborated our theoretical findings on the enhanced superconducting transition temperature of TaSe2,found to be increased by 20-folds(?3k)using low transport experiments.Employing synchrotron radiation-based characterizations,we established the occurrence of charge transfer from the Sn atoms to TaSe2.Altogether,the coexistence of these properties makes Sn0.5TaSe2 a potential candidate for topological superconductivity.Also,we intercalate Cr into TaSe2.We found that Cr could induce a phase transition from a metallic to a semiconducting phase through a low-temperature transport experiment.Cr spin polarizing electrons produced a mixed state which changes the spin ordering.Through the temperature-dependent magnetic experiment,an inducement of paramagnetism with a Curie temperature of?50K in the Cr0.05TaSe2 single-crystal is observed.In the third study,we were able to modulate and study the nature of the Charge density wave(CDW)phase in 1T-TiSe2.We synthesized SnxTiSe2 single-crystals via the Chemical vapor transport technique.The electronic properties were studied using the synchrotron radiation-based angle-resolved photoemission spectroscopy(ARPES)to understand the evolution of the CDW mechanism by injecting charges facilitated through Sn intercalation in TiSe2.The CDW phase in 1T-TiSe2 is observed to be gradually suppressed with an increase in charge transfer.A Jahn-Teller(JT)-like a downward Se shift of 4p valence band,was observed in the temperature-dependent ARPES results.We suggest the JT mechanism as the driving mechanism and the most subtle way to explain the CDW formation mechanism in the pristine and Sn intercalated 1T-TiSe2 system.