http://localhost:8081/jspui/handle/123456789/37 2026-05-07T21:22:04Z http://localhost:8081/jspui/handle/123456789/20528 Title: Study of Hydrodynamical Behaviour and Transport Properties of Hot QCD Medium Authors: Pushpa Abstract: The primary focus of this thesis is two-fold: a) Studying the linearly stable and causal theory of relativistic third-order viscous hydrodynamics, b) A comprehensive investigation of the charge, heat, and momentum response in a hot QCD medium (called quark gluon plasma (QGP)) in the presence of a weak background constant magnetic field. A novel state of quark matter (deconfined soup of quarks and gluons) is expected to form at extremely high temperature and/or density during the ultra-relativistic heavy-ion collisions (URHICs). Under such extreme conditions, quark matter may approach local thermodynamic equilibrium, allowing the exploration of various phases as well as thermodynamic and transport properties of hot QCD medium. Determining the transport properties of this hot QCD medium formed from heavy-ion collisions (HICs) is challenging due to the lack of direct observation. Experimentally, only the energy and momenta of the particles generated in the final stages of a collision after hadronization can be observed, by which time the hot hadronic matter has cooled and become non-interacting. Therefore, to investigate the thermodynamic and transport properties of the hot QCD medium, it is necessary to model the entire heavy-ion collision process from beginning to end. The dynamic evolution of the deconfined hot QCD medium and the subsequent hot hadronic matter can be characterised using the laws of fluid dynamics, assuming that the system stays near local thermodynamic equilibrium during its evolution. Fluid dynamics, also referred to as hydrodynamics, is an effective technique for describing a system using macroscopic variables such as local energy density, pressure, temperature, and flow velocity. The earliest theoretical formulation of relativistic first- and ix x second-order dissipative hydrodynamics is well established. In the present thesis, we have formulated a linearly stable and causal theory of relativistic third-order viscous hydrodynamics from the kinetic theory in relaxation-time approximation (RTA). We have used the Chapman-Enskog-like iterative approach to solve the Boltzmann equation and obtain the dissipative correction to the distribution function. We have also demonstrated the linear stability and causality of the present formulation by considering perturbations around a global equilibrium state. 2024-09-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20525 Title: ELECTRONIC STRUCTURE, MAGNETISM AND TOPOLOGICAL PROPERTIES OF CERTAIN Eu BASED LAYERED MATERIALS Authors: Choudhury, Amarjyoti Abstract: This thesis explores the unique characteristics of the materials where electrons ex hibit unconventional behavior, particularly those with linear band dispersion near the Fermi level (FL). The quasi-particle excitations near band crossing points replicate the characteristics of relativistic Dirac or Weyl fermions and demonstrate resistance to perturbations due to the symmetry protection of topology. The intertwining of magnetism with band topology, introduces intriguing electronic band structures with topologically non-trivial properties, often leading to novel magnetic phenomena which have immense potential for applications in spintronics and quantum computing. Mag netism in condensed matter, originating from quantum mechanics, stands as a pivotal domain in both fundamental and applied physics research. The diverse behaviors exhibited by magnetic materials in response to external magnetic fields underpin es sential applications in devices like magnetic memory, spintronics, giant magnetore sistance, and beyond. In solids, the cornerstone of magnetism lies in ions harboring unpaired electrons, characterized by non-zero magnetic moments. These ions exhibit markedly distinct phenomena when they are in proximity and able to interact with each other, in contrast to their behavior when isolated or non-interacting. This un derscores the diverse range of magnetic moment interactions, specifically exchange interactions, which give rise to the myriad of magnetic properties observed in solids. 2024-06-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20513 Title: EXPLORING HYSTERESIS IN CURRENT-VOLTAGE CHARACTERISTICS OF HALIDE PEROVSKITES: MECHANISMS AND IMPLICATIONS Authors: Deepak Abstract: Hybrid halide perovskites have garnered significant interest for optoelectronic devices due to their remarkable optical properties and cost-effective synthesis. However, their full potential remains limited by an incomplete understanding of their electrical behavior. This thesis investigates the impact of grain structure on hysteresis in CsPbBr3 perovskite materials. Current-voltage characteristics are analyzed for single-grain nanocrystals (SG-NCs), multigrain nanocrystals (MG NCs), and polycrystalline thin films (PTFs) under varying scan rates and illumination. The results demonstrate extensive hysteresis across a broad voltage range in PTFs, attributed to grain boundaries facilitating ion migration. Conversely, SG-NCs exhibit minimal hysteresis limited to a narrow voltage window, suggesting polarization and ion confinement within the nanocrystals. Interestingly, MG-NCs display a combination of long- and short-range hysteresis due to the presence of internal grain boundaries while maintaining some degree of ion confinement. These findings establish a clear correlation between grain boundaries and hysteresis behavior, providing valuable insights into charge transport mechanisms within perovskite materials. Building upon the understanding of hysteresis, this thesis also delves into the switching mechanism of halide perovskite memristors, aiming to exploit their hysteresis for information storage and brain-inspired computing, by exploring the current-voltage characteristics and impedance spectroscopy of ITO/MAPbBr3/Au devices to analyze the SET-RESET states under varying light intensities and applied biases. The results suggest a clear correlation between increased light power and a shift in the SET voltage, indicating the involvement of electronic-ionic coupling and light-induced ion migration. Additionally, impedance spectroscopy reveals a negative slope in the AC conductivity at the SET state, particularly at low frequencies. This phenomenon is attributed to the presence of an ion-induced voltage that gets progressively screened by photogenerated charge carriers under illumination. These findings provide valuable insights into the switching mechanism of perovskite memristors, paving the way for their development as high-performance memory devices for neuromorphic computing applications. 2024-05-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20512 Title: SURFACE PLASMON/PHONON RESONANCE-BASED OPTICAL SENSORS Authors: Uwais, Mohd Abstract: Surface plasmon resonance (SPR) has attracted great attention and substantially contributed to sensing applications in recent years. The salient features of SPR-based sensors, such as quick and label-free detection, high sensitivity, small sample size, simple structure, reliable results at a reasonable cost, and smooth operation, make them an excellent tool for sensing applications in the field of chemical sensing, environment monitoring, medical diagnosis, and biosensing. SPR phenomenon occurs at the metal-dielectric interface and can be realized using special phase-matching schemes such as prism and grating coupling techniques. High optical losses and very large negative permittivity of the metals at longer wavelengths limit the use of the SPR beyond the NIR-spectral ranges. Polar dielectric materials serve as an alternative to metals, providing low optical loss and a functional spectral range from mid-IR to THz. The surface phonon resonance (SPhR) phenomenon takes place at the polar dielectric material-dielectric interface in a particular wavelength range known as the reststrahlen band. Similar to SPR, SPhR also offers potential applications such as surface-enhanced infrared absorption, coherent thermal emission, and refractive index sensing. In this thesis, we numerically presented and analyzed the SPR and SPhR-based refractive index sensors. The reflection dip shift observed in the SPR and SPhR response curves, due to a small change in the refractive index of the analyte, serves as the basic premise underlying refractive index sensing. A higher resolution of the sensor is correlated with a smaller width of the reflection dip, allowing for more accurate detection of changes in the refractive index. First, we designed a highly sensitive SPhR-based refractive index sensor in the mid-IR wavelength range. The structure of this sensor contains an Au grating on the polar dielectric material SiC substrate, which supports the excitation of the surface phonon polaritons. The numerical simulations of the sensor are carried out using RCWA to investigate the performance of the sensor in terms of sensitivity, quality factor, and detection accuracy. The optimized value of the grating depth provides the maximized performance of 7066.67 nm/RIU for sensitivity, 225.1 RIU-1 for the quality factor, and 6.75 for detection accuracy. The study, including other polar dielectric materials in the proposed structure, shows that the performance of the sensor can be further improved using the polar dielectric materials of high wavelength reststrahlen band. 2024-06-01T00:00:00Z