Jit Sarkar

Quantum and classical contributions to linear magnetoresistance in topological insulator thin films

Three dimensional topological insulators possess backscattering immune relativistic Dirac fermions on their surface due to nontrivial topology of the bulk band structure. Both metallic and bulk insulating topological insulators exhibit weak-antilocalization in the low magnetic field and linear like magnetoresistance in higher fields. We explore the linear magnetoresistance in bulk insulating topological insulator Bi2-xSbxTe3-ySey thin films grown by pulsed laser deposition technique. Thin films of Bi2-xSbxTe3-ySey were found to be insulating in nature, which conclusively establishes the origin of linear magnetoresistance from surface Dirac states. The films were thoroughly characterized for their crystallinity and composition and then subjected to transport measurements. We present a careful analysis taking into considerations all the existing models of linear magnetoresistance. We comprehend that the competition between classical and quantum contributions to magnetoresistance results in linear magnetores...

Investigation of mechanical properties and deformation behavior of single-crystal Al-Cu core-shell nanowire generated using non-equilibrium molecular dynamics simulation

Molecular dynamics (MD) simulation studies were carried out to generate a cylindrical single-crystal Al-Cu core-shell nanowire and its mechanical properties like yield strength and Young’s modulus were evaluated in comparison to a solid aluminum nanowire and hollow copper nanowire which combines to constitute the core-shell structure respectively. The deformation behavior due to changes in the number of Wigner-Seitz defects and dislocations during the entire tensile deformation process was thoroughly studied for the Al-Cu core-shell nanowire. The single-crystal Al-Cu core-shell nanowire shows much higher yield strength and Young’s modulus in comparison to the solid aluminum core and hollow copper shell nanowire due to tangling of dislocations caused by lattice mismatch between aluminum and copper. Thus, the Al-Cu core-shell nanowire can be reinforced in different bulk matrix to develop new type of light-weight nanocomposite materials with greatly enhanced material properties.

Evidence of charged puddles and induced dephasing in topological insulator thin films

We investigate the dephasing mechanism in bulk insulating topological insulator thin films. The phase coherence length is extracted from magnetoresistance measurements at different temperatures. There is a crossover of the phase coherence length as a function of temperature signifying the role of more than one dephasing mechanism in the system. The dephasing rates have been studied systematically and explained.We investigate the dephasing mechanism in bulk insulating topological insulator thin films. The phase coherence length is extracted from magnetoresistance measurements at different temperatures. There is a crossover of the phase coherence length as a function of temperature signifying the role of more than one dephasing mechanism in the system. The dephasing rates have been studied systematically and explained.

Graphene–magnesium nanocomposite: An advanced material for aerospace application

This work focuses on the analytical study of mechanical and thermal properties of a nanocomposite that can be obtained by reinforcing graphene in magnesium. The estimated mechanical and thermal properties of graphene–magnesium nanocomposite are much higher than magnesium and other existing alloys used in aerospace materials. We also altered the weight percentage of graphene in the composite and observed mechanical and thermal properties of the composite increase with increase in concentration of graphene reinforcement. The Young’s modulus and thermal conductivity of graphene–magnesium nanocomposite are found to be ≥165xa0GPa and ≥175xa0W/mK, respectively. Nanocomposite material with desired properties for targeted applications can also be designed by our analytical modeling technique. This graphene–magnesium nanocomposite can be used for designing improved aerospace structure systems with enhanced properties.

Evaluating the effect of different test parameters on the tensile mechanical properties of single crystal silver nanowires using molecular dynamics simulation

Nanowires show amazing mechanical properties with respect to their bulk counterpart owing to their very high specific surface and/or interface area and, thus, are widely studied among several researchers. But it is difficult to study the mechanical properties of nanowires at atomistic level, and computational tools provide the required solution. Molecular dynamics simulation studies were carried out in this work to evaluate the mechanical properties of single crystal silver nanowire subjected to tensile deformation under varying wire diameter (4–14xa0nm), test temperature (100–500xa0K), and strain velocity (1–6xa0Å/ps). The simulation were carried out in analogous to real experiment, and the engineering stress and strain were calculated from the simulation result of load and displacement data. The mechanical properties like yield strength and Young’s modulus were calculated from the engineering stress-strain curve. The effect of different test parameters like wire diameter, equilibration temperature, and strain velocity on the mechanical properties were also thoroughly investigated. The result shows that single crystal silver nanowire shows excellent mechanical properties and, thus, can be used as a reinforcing agent to develop ultra-high strength advanced materials for defense and aerospace applications.

Molecular dynamics study of defect and dislocation behaviors during tensile deformation of copper-silver core-shell nanowires with varying core diameter and shell thickness

Core-shell type nanostructures have drawn much attention among material researchers as they exhibit exceptional properties due to their unique structure. Among different core-shell nanostructures, copper-silver core-shell nanostructures are widely investigated in recent days for exhibiting different unique properties like very high mechanical strength. Molecular dynamics simulations were carried out to investigate the underlying deformation mechanism during tensile testing of copper-silver core-shell nanowires with varying core diameter and shell thickness. The Wigner-Seitz defect analysis was used to calculate the total number of point defects like vacancies and interstitials during the entire deformation process. The type, number, and total length of dislocation segments were thoroughly investigated throughout the different stages of deformation. The effects of varying core diameter and shell thickness on the defect and dislocation configurations were also studied. Thus, this study helps us to understand the underlying mechanisms or factors that contribute to the ultra-high strength and mechanical properties of Cu-Ag core-shell nanowires with varying core diameter and shell thickness.

Comparison of mechanical properties of silicene estimated using different testing procedures: A molecular dynamics study

Silicene, a two-dimensional allotrope and silicon counterpart of graphene, has recently attracted scientists all over the world due to its superior material properties and thus can be a potential applicant as a reinforcing agent. The mechanical properties of silicene have been studied using several testings (tensile, bending, oscillation, and equilibrium) through the molecular dynamics (MD) simulation technique. Plastic flow occurs, and 46% elongation is observed in a silicene sheet with dimensions of (200u2009×u2009700) A for room temperature (298u2009K) tensile testing. The yield strength, ultimate tensile strength, Youngs modulus (E), cohesive energy, and bulk modulus are found to be 18.28u2009GPa, 23.96u2009GPa, 5.25 TPa, 3.72u2009eV atom−1, and 3.62 TPa, respectively. For the same sample, a Poisson ratio of 0.75 is observed. An ultrahigh mechanical strength of silicene, even higher than the previously predicted value of 0.178 TPa, is observed in this study.

Bulk saturable absorption in topological insulator thin films

We present nonlinear optical absorption properties of pulsed laser deposited thin films of topological insulator (TI), Bi2Se3 on a quartz substrate, using an open aperture z-scan technique. We observed saturable absorption with a low saturation intensity in as deposited thin films. Past results from the literature are inconclusive in establishing whether the saturable absorption in TI is coming from surface states or the bulk. Specifically designed experiments with magnetically doped TI samples allow us to attribute the saturable absorption characteristic of TI to the bulk states. Detailed experimental procedures and possible explanation of observed results have been discussed.